An explanataion of what this term means.
An Ostinato is a phrase that repeats over and over within a piece of music. In drum kit terms this could be the feet played underneath a rudiment in an exercise, a Four On The Floor style kick in a groove or any other idea where a short rhythmic pattern is repeated over and over whilst other things are happening. In relation to modern rock/pop songs an ostinato is generally reffered to as a riff. Wikipedia has a good article on this subject that has audio extracts showing examples of ostinatos used within songs.
Below I have given a couple of written examples of drum kit parts where ostinati are used in different ways. In this first version the feet are playing a simple quarter note pattern that is repeated under all eight bars whilst the hands play a rhythmic pattern over the drums.
In this version the ostiatno is the right hand rhythm played on the ride. The kick and snares then do there thing around this.
Ostinati are an important concept to drummers, particularly when soloing. The main job of a drummer within a band is to keep time and using a simple ostinato to do that will allow you to be more musical within this role.