Military
Etymology and definitions: The first recorded use of the word "military" in English, spelled militarie, was in 1582. It comes from the Latin militaris (from Latin miles 'soldier') through French, but is of uncertain etymology, one suggestion being derived from *mil-it- – going in a body or mass.
As a noun phrase, "the military" usually refers generally to a country's armed forces, or sometimes, more specifically, to the senior officers who command them. In general, it refers to the physicality of armed forces, their personnel, equipment, and the physical area which they occupy.
As an adjective, military originally referred only to soldiers and soldiering, but it broadened to apply to land forces in general, and anything to do with their profession. The names of both the Royal Military Academy (1741) and United States Military Academy (1802) reflect this. However, at about the time of the Napoleonic Wars, military began to be used in reference to armed forces as a whole, such as "military service", "military intelligence", and "military history". As such, it now connotes any activity performed by armed force personnel.

History: Military history is often considered to be the history of all conflicts, not just the history of the state militaries. It differs somewhat from the history of war, with military history focusing on the people and institutions of war-making, while the history of war focuses on the evolution of war itself in the face of changing technology, governments, and geography.
Military history has a number of facets. One main facet is to learn from past accomplishments and mistakes, so as to more effectively wage war in the future. Another is to create a sense of military tradition, which is used to create cohesive military forces. Still, another is to learn to prevent wars more effectively. Human knowledge about the military is largely based on both recorded and oral history of military conflicts (war), their participating armies and navies and, more recently, air forces.

Organization: 

Personnel and units: Despite the growing importance of military technology, military activity depends above all on people. For example, in 2000 the British Army declared: "Man is still the first weapon of war."

Rank and role: The military organization is characterized by a command hierarchy divided by military rank, with ranks normally grouped (in descending order of authority) as officers (e.g. colonel), non-commissioned officers (e.g. sergeant), and personnel at the lowest rank (e.g. private). While senior officers make strategic decisions, subordinated military personnel (soldiers, sailors, marines, or airmen) fulfil them. Although rank titles vary by military branch and country, the rank hierarchy is common to all state armed forces worldwide.
In addition to their rank, personnel occupy one of many trade roles, which are often grouped according to the nature of the role's military tasks on combat operations: combat roles (e.g. infantry), combat support roles (e.g. combat engineers), and combat service support roles (e.g. logistical support).

Recruitment: Personnel may be recruited or conscripted, depending on the system chosen by the state. Most military personnel are males; the minority proportion of female personnel varies internationally (approximately 3% in India, 10% in the UK, 13% in Sweden, 16% in the US, and 27% in South Africa). While two-thirds of states now recruit or conscript only adults, as of 2017 50 states still relied partly on children under the age of 18 (usually aged 16 or 17) to staff their armed forces.
Whereas recruits who join as officers tend to be upwardly-mobile, most enlisted personnel have a childhood background of relative socio-economic deprivation. For example, after the US suspended conscription in 1973, "the military disproportionately attracted African American men, men from lower-status socioeconomic backgrounds, men who had been in nonacademic high school programs, and men whose high school grades tended to be low". However, a study released in 2020 on the socio-economic backgrounds of U.S. Armed Forces personnel suggests that they are at parity or slightly higher than the civilian population with respect to socio-economic indicators such as parental income, parental wealth and cognitive abilities. The study found that technological, tactical, operational and doctrinal changes have led to a change in the demand for personnel. Furthermore, the study suggests that the most disadvantaged socio-economic groups are less likely to meet the requirements of the modern U.S. military.

Obligations: The obligations of military employment are many. Full-time military employment normally requires a minimum period of service of several years; between two and six years is typical of armed forces in Australia, the UK and the US, for example, depending on role, branch, and rank. Some armed forces allow a short discharge window, normally during training, when recruits may leave the armed force as of right. Alternatively, part-time military employment, known as reserve service, allows a recruit to maintain a civilian job while training under military discipline at weekends; he or she may be called out to deploy on operations to supplement the full-time personnel complement. After leaving the armed forces, recruits may remain liable for compulsory return to full-time military employment in order to train or deploy on operations.
Military law introduces offences not recognized by civilian courts, such as absence without leave (AWOL), desertion, political acts, malingering, behaving disrespectfully, and disobedience (see, for example, offences against military law in the United Kingdom). Penalties range from a summary reprimand to imprisonment for several years following a court martial. Certain rights are also restricted or suspended, including the freedom of association (e.g. union organizing) and freedom of speech (speaking to the media). Military personnel in some countries have a right of conscientious objection if they believe an order is immoral or unlawful, or cannot in good conscience carry it out.
Personnel may be posted to bases in their home country or overseas, according to operational need, and may be deployed from those bases on exercises or operations. During peacetime, when military personnel are generally stationed in garrisons or other permanent military facilities, they conduct administrative tasks, training and education activities, technology maintenance, and recruitment.

Training: Initial training conditions recruits for the demands of military life, including preparedness to injure and kill other people, and to face mortal danger without fleeing. It is a physically and psychologically intensive process which resocializes recruits for the unique nature of military demands. For example:

Individuality is suppressed (e.g. by shaving the head of new recruits, issuing uniforms, denying privacy, and prohibiting the use of first names);
Daily routine is tightly controlled (e.g. recruits must make their beds, polish boots, and stack their clothes in a certain way, and mistakes are punished);
Continuous stressors deplete psychological resistance to the demands of their instructors (e.g. depriving recruits of sleep, food, or shelter, shouting insults and giving orders intended to humiliate)
Frequent punishments serve to condition group conformity and discourage poor performance;
The disciplined drill instructor is presented as a role model of the ideal soldier.

Intelligence: The next requirement comes as a fairly basic need for the military to identify possible threats it may be called upon to face. For this purpose, some of the commanding forces and other military, as well as often civilian personnel participate in identification of these threats. This is at once an organization, a system and a process collectively called military intelligence (MI). Areas of study in Military intelligence may include the operational environment, hostile, friendly and neutral forces, the civilian population in an area of combat operations, and other broader areas of interest.
The difficulty in using military intelligence concepts and military intelligence methods is in the nature of the secrecy of the information they seek, and the clandestine nature that intelligence operatives work in obtaining what may be plans for a conflict escalation, initiation of combat, or an invasion.
An important part of the military intelligence role is the military analysis performed to assess military capability of potential future aggressors, and provide combat modelling that helps to understand factors on which comparison of forces can be made. This helps to quantify and qualify such statements as: "China and India maintain the largest armed forces in the World" or that "the U.S. Military is considered to be the world's strongest".

Although some groups engaged in combat, such as militants or resistance movements, refer to themselves using military terminology, notably 'Army' or 'Front', none have had the structure of a national military to justify the reference, and usually have had to rely on support of outside national militaries. They also use these terms to conceal from the MI their true capabilities, and to impress potential ideological recruits.
Having military intelligence representatives participate in the execution of the national defence policy is important, because it becomes the first respondent and commentator on the policy expected strategic goal, compared to the realities of identified threats. When the intelligence reporting is compared to the policy, it becomes possible for the national leadership to consider allocating resources over and above the officers and their subordinates military pay, and the expense of maintaining military facilities and military support services for them.

Economics: Defense economics is the financial and monetary efforts made to resource and sustain militaries, and to finance military operations, including war.
The process of allocating resources is conducted by determining a military budget, which is administered by a military finance organization within the military. Military procurement is then authorized to purchase or contract provision of goods and services to the military, whether in peacetime at a permanent base, or in a combat zone from local population.