A short-term relationship (STR) is a relationship that may not last a long time. Includes a causal relationship, an affair and possibly a one-night stand. For men, the sex in a short-term relationship is usually more exciting than in a long-term relationship due to increased perceived mutual attraction and sexual variety. For women, the sex in a short-term relationship is more exiting because they could be more hypergamous in their choice of men.
There isn't any agreement on the duration of a short-term relationship. Some define the duration to last a few days while others define it to last a few months. It may or not may be monogamous. The frequency of sex may be once per day, or once in a few months (as in having casual sex once so often with a "friend").
Short-term relationships don't last very long because the male is more attractive and he ends up having sex with someone else or dumping her. Thus, a short-term relationship could be conceived a code word for a hypergamous relationship in which the male is higher in league than the female.
However, its possible for a short-term relationship to reinitiate (such as in the case of a female returning to have sex with the same slayer whenever she breaks up with her boyfriend; an on-again, off-again relationship with a slayer). In this sense, a short-term relationship could be viewed in a misnomer because the female will remain "friends" with the slayer long after they stopped having sex.
When one searches "friends with benefits" or "fuck buddy" on Google, you will get articles on "advice" for initiating or maintaining such a relationship. A vast majority of these articles are written by women. The vast majority of the comments in these articles are made by women too. This shows how skewed casual sex is for women. It's easy for a woman to have a "friends with benefits" type of relationship. But for a man, this impossible unless you're one of the top men.
The results: The top 2.6% of men are responsible for 29% of the hookups. The top 5.4% are responsible for 40% of the hookups. The top 28% of the men are responsible for 78% of the hookups. These statistics are for Fall 2010.