- This article concerns man in the sense of "human male". For other meanings of man see Man (disambiguation).
A man is a male human adult, in contrast to an adult female, which is a woman. The term man (irregular plural: men) is a term used to indicate either a person generally, or a male person specifically.
The term "man" (from Proto-Germanic mannaz "man, person") and words derived from can designate any or even all of the human race regardless of their gender or age. This is indeed the oldest usage of "man".
The word developed into Old English man, mann "human being, person," (cf. also German Mann, Old Norse mağr, Gothic manna "man").
It is derived from a PIE base *man- (cf. Sanskrit/Avestan manu-, Russian muzh "man, male"). Sometimes, the word is connected with the root *men- "to think" (cognate to mind). Restricted use in the sense "adult male" only began to occur in late Old English, around 1000 AD, and the word formerly expressing male sex, wer had died out by 1300 (but survives in e.g. were-wolf and were-gild). The original sense of the word is preserved in mankind, from Old English mancynn.
In Old English the words wer and wyf (also wæpman and wifman ) were what was used to refer to "a man" and "a woman" respectively, and "man" was gender neutral. In Middle English man displaced wer as term for "male human," whilst wyfman (which eventually evolved into woman) was retained for "female human." Man does continue to carry its original sense of "Human" however, resulting in an asymmetry sometimes criticized as sexist. 
In the 20th century, the generic meaning of "man" declined still further (but survives in compounds "mankind", "everyman", "no-man", etc), and it is probable that future generations will see it as totally archaic, and use it solely to mean "adult male". Interestingly, exactly the same thing has happened to the Latin word homo: in the Romance languages, homme, uomo, hombre, homem etc. have all come to refer mainly to males, with residual generic meaning.
Manhood is the period in a male's life after he has transitioned from a boy. Many cultures have rites of passage to symbolize a man's coming of age, such as confirmation in some branches of Christianity, bar mitzvah in Judaism, or even just the celebration of the eighteenth or twenty-first birthday.
A boy is a male human child, in contrast to an female child, which is a girl. The term boy is used to indicate biological sex distinctions, cultural gender role distinctions, or both. After a boy matures, he is called a man. There are various colloquial exceptions to this usage. For example, the word boy is also commonly used when discussing adult males in relationships, such as in the word boyfriend. Sometimes the word is also used disparagingly, or as a term of familiarity (particularly in the US south).
For many, the word man implies a certain degree of maturity and responsibility that young men in particular often feel unprepared for; yet they may also feel too old to be called a boy. For this reason, many avoid using either man or boy to describe a young man and prefer colloquial terms such as bloke, chap, fellow, guy or the like.
In terms of sex, men have various sexual characteristics that differentiate them from women. Just as in women, the sex organs of a man are part of the reproductive system, consisting of the penis, testicles, vas deferens and other sperm cords, and the prostate gland. The male reproductive system is oriented around producing and ejaculating semen which carries sperm and thus genetic information. Since sperm that enters a woman's uterus and then fallopian tubes goes on to fertilize an egg which develops into a fetus or child during gestation, men play no further necessary role in the creation of offspring. The concept of fatherhood, though, exists in every human society.
The secondary sex characteristics, such as body hair and muscle growth, are involved in attracting a mate or in defeating rivals. But these secondary traits are also often related to reproduction in some manner. In contrast to women, men have sex organs that are mostly considered to be external, although many parts of the male reproductive system are internal as well (such as the prostate). The study of male reproduction and associated organs is called andrology. Most, but not all, men have the karyotype 46/XY.
In general, men suffer from many of the same illnesses as women. However, there are some sex-related illnesses that occur only, or more frequently, in men. For example, autism and color blindness are more common in men than women. As well, some age-related disorders such as Alzheimer's disease appear to be more common among men, though whether this is due to a genuinely higher incidence or because men have lower life expectancies than women is uncertain.
Biological factors are usually not the sole determinants of whether a person considers themselves as man or is considered a man or not. For example, several men have been born without a typical male physiology (that is, they are transgendered or transsexual men; estimates range between 1:2.000 and one in 100,000), or some men can have an abnormal hormone or chromosomal difference (such as androgen insensitivity syndrome), or another intersex condition; some of those intersex people who have had a female sex assigned at birth sought to reassign their sex later in their lives (or vice versa). (See also gender identity, gender role and transman.)
Additionally, 20% of males, particularly in the U.S., the Philippines, and South Korea, as well as Jews and Muslims from all countries, have experienced circumcision, a process of altering the penis from its natural state by removing the foreskin.
An estimated 1% to about 5-10% of all men are mostly or exclusively homosexual, meaning that they prefer sexual and/or romantic relationships with other men. Smaller percentages consider themselves bisexual. Significant numbers of men who otherwise identify as heterosexual have engaged in non-heterosexual behavior. Overlaps exist between these identities and their nature is a subject of controversy.
In terms of gender, men differ from women by a variety of behaviours. Certain characteristics generally associated with men may be delineated; it is important to remember that the following are generalizations (even stereotypes) and are by no means true of all men.
Men are often considered to be more:
aggressive than women. However, in interpersonal relationships, most research has found that men and women are equally aggressive. Men do tend to be more aggressive outside of the home.
courageous and adventuresome than women; the negative side of this image is the perception that men may be more prepared to abandon their families.
competitive but also more stubborn than women.
self-confident (even arrogant) and exhibit better leadership skills than women.
self-controlled and less emotional (sometimes to the point of being perceived as cold and unloving) than women.
technically and organizationally skilled than women.
- prone to abstract thinking than women
In terms of outward appearance, few men in Western cultures wear cosmetics or clothing generally associated with female gender roles. (Doing so is known as cross-dressing, and is generally stigmatised.) Fashions change, however: whereas wearing jewelry was formerly associated with females, today in Western cultures it is common for men to wear earrings without being perceived as cross-dressing. The same has become true of the shaving off of unwanted body and facial hair, though removal of the latter has long been common among men in many cultures.