> koalamom,whose parents did *not* get their money's worth out of six years of music lessons, apparently, because she'd never heard of an 'ostinato' before this post.

An ostinato is basically a short rhythm or snippet of music that is played repetitively in a piece of music as a foundation for the music. Usually other stuff is layered on top of it. For example, the "bump, bump, bump-bump" in the Mission Impossible theme could be considered an ostinato.