n (sport 体) line marking each end of the court in tennis or the boundary of the running track in baseball （网球场的）底线; （棒球场的）垒线. =>illus at tennis 见tennis之插图.

n [C usually singular]
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.
the line at the back of the court in games such as tennis or volleyball
the area that a player must run within, on a baseball field