service line

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A line, as on a tennis or handball court, marking the area into which or from which serves must be directed.

from The Century Dictionary.

• noun In lawn-tennis, one of the two lines drawn across the court twenty-one feet from the net. See lawn-tenns.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun tennis, badminton The line, in tennis and similar sports, behind which the ball is initially served and over which the feet must not cross when serving

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the back line bounding each end of a tennis or handball court; when serving the server must not step over this line