In musical terminology, a bar is a segment of time defined as a given number of beats of a given duration. It is used the same as measure. A bar line is the line which lies between or separates bars. While many see bars and bar lines as arbitrary, others feel otherwise: "The bar line is much, much more than a mere accent, and I don't believe that it can be simulated by an accent, at least not in my music." - Igor Stravinsky (DeLone et. al. (Eds.), 1975, chap. 3).
References
DeLone et. al. (Eds.) (1975). Aspects of Twentieth-Century Music. Englewood Cliffs, New Jersey: Prentice-Hall. BooksEnthsiast.com.
