base ‧ line /ˈbeɪslaɪn/ BrE AmE noun [countable usually singular]
1 . technical a standard measurement or fact against which other measurements or facts are compared, especially in medicine or science:
The company’s waste emissions were 14% lower than in 1998, the baseline year.
2 . the line at the back of the court in games such as tennis or ↑ volleyball
3 . the area that a player must run within, on a ↑ baseball field