Home run Simply put, a home run is sexual intercourse Grand slam Those looking to excel at sexual baseball strive for the grand slam.Strike out A strike out is when you don't get a kiss at the end of the evening.
To use the expression correctly, you get or make it to a base, per my comment: quotation, if I interpret it correctly, they had intravaginal sex twice and then she performed oral sex on him.
Although this wasn't what "House" referred to, Urban Dictionary lists fifth base as anal sex.
There are, as the top comment on this question notes, four bases in baseball, and these have corresponding sex acts associated with them.
"I got to second base with that girl yesterday." "I didn't think I had a chance, but I made it to third base with her last night." One of the other answers has provided a nice link to the Wikipedia entry for baseball metaphors for sex.
It also includes other forms of petting, touching and groping.
Third base may include manual or oral sex for either partner.