A gay bottom is the partner who is anally penetrated in gay anal sex.
During gay anal sex a gay bottom is the partner who is penetrated. Bottoms are also referred to as passive. Being a gay bottom does not necessarily mean that a man is submissive or a less aggressive sexual partner nor does it in any way mean that the bottom is feminine or playing a female role in sex. Bottom can also be used as a verb.
There is no "right" position for a gay bottom to use during anal intercourse. Both the position during anal sex and the amount of motion is entirely up to the person and his partner. In some cases, a man who prefers to bottom will top with the right partner. Due to the location of the prostate gland in human males, being ass fucked can be quite pleasurable or even lead to orgasm or a bottom may masturbate himself or his cock may be stroked by his partner during sex.
Sometimes the phrase "bottom" or gay bottom may also refer to the more submissive partner in a gay relationship or the submissive during BDSM encounters. The term bottom is sometimes used in BDSM or lesbian relationships as well.