A term for a section of instruments in a marching band or drum corps. There is a trumpet line, a drum line, a trombone line, etc. Simply using the term "line" requires that the context is sufficiently established in the conversation so as to indicate to which instrument the speaker is referring. A line is also a vauge word for a musical phrase or musical idea, as in "the trumpets have this one line that hits the E above high C," or "in measure X the violin and cello lines start to interweave." If there is an official use of "line" in this way, I don't know what it is.