The phrase "old sheet music" refers to printed or written musical compositions that were popular in a previous era. These are typically out-of-print pieces, which means they are no longer being produced or distributed by the original publisher. Old sheet music can be found in antique shops, flea markets, and online auction sites, among other places. They often feature beautiful artwork and intricate designs on their covers, making them collector's items for some people. The phrase is typically used to describe a physical object - an old piece of paper with musical notation written or printed on it.