1. [ noun ] an imaginary line or standard by which things are measured or compared

"the established a baseline for the budget"

Related terms: standard
2. [ noun ] (tennis) the back line bounding each end of a tennis or handball court; when serving the server must not step over this line
Synonyms: service_line
Related terms: line
3. [ noun ] (baseball) the lines a baseball player must follow while running the bases
Related terms: line