“The bases” is a baseball metaphor to refer to the different levels of sexual intimacy. It is popular among American teenagers. Its usage began right after World War II. First base involves kissing and holding hands. Second base may involve touching or rubbing genitals through clothes. Third base gets a little hotter with mutual masturbation and oral sex. A home run is going “all the way.”
More About The Bases
“The bases” is not the only baseball metaphor popularly used in American culture. There is also “pitching” where a man performs anal sex. “Catching” is where a man receives anal sex. Then, the “strikeout” is where zero sexual engagement – not even first base – is achieved. The use of these terms is reflective of Western popular culture.