third base
noun [ C usually singular ] uk/ˌθɜːd ˈbeɪs/ us/ˌθɝːd ˈbeɪs/ (also informal third)
（棒球场上的）三垒
the third place a baseball player has to touch in order to score, or the position near this place played by a member of the team in the field
Idiom
get to third baseidiom US informal触摸性伙伴的生殖器
to touch a partner's genitals (= sexual organs)