Homosexual behavior is sexual contact between two people or animals of the same sex, i.e., two males or between two females. Homosexual behavior can vary from non-consequential, incidental acts to full-fledged homosexual acts. The former are excusable and often serve other purposes, while the latter are genuine displays of homosexual longing and an espousal of the homosexual lifestyle. The distinction lies in the intent: some homosexual behavior is homosexual only on the technical ground that it involves animals or people of the same sex, but the purpose of the behavior is not intrinsically linked to the involvement of two people of the same sex.
If a male animal (such as a ruminant) mounts another male, it is not necessarily a homosexual act; instead it is just dominance behavior or possibly the result of poor vision leading to a case of mistaken identity. The act of mounting is a dominant act, irrespective of the sex of the mounted animal -- the act is "homosexual" solely on the technical ground that it involves two bulls, but it is not homosexual because the bulls are not do not display an intent that the mounted be male.
A commonly seen example in people is one athlete patting the backside of another athlete on his team. In the literal sense of the word, this is "homosexual" behavior since it involves two people of the same sex, yet it is not a homosexual act since the intent of the act was not linked to the person being male, but rather to the person being a teammate. If one were to follow the technical definition of "homosexual" then all sorts of everyday acts would be considered "homosexual behavior", such as grappling in wrestling or getting changed in a same-sex locker room. But clearly these acts are not homosexual because they are incidentally between people of the same sex, not intentionally and with ulterior motives.
The Roman Catholic Church makes a distinction between harboring homosexual inclination (or orientation) and actually acting upon that inclination. Thus, it deems the former acceptable while joining most other Christians as well as Jews in condemning the latter as sinful. Muslims simply publicly hang homosexuals, no matter what age they are.