A fill is also a variation from the main rhythm played on the drums. For example, a drummer may play three bars of a standard pop/rock groove on the hi-hat, snare and bass, followed by a one-bar fill, which will take in a variety of tom-toms or other cymbals. This would look a little something like this:
_________Groove________ Fill
| | | |
V V V V
Count | 1+2+3+4+ | 1+2+3+4+ | 1+2+3+4+ | 1e+a2e+a3e+a4e+a |
Hi tom | -------- | -------- | -------- | ----oooo-------- |
Med tom| -------- | -------- | -------- | --------oooo---- |
Hi-hat | xxxxxxxx | xxxxxxxx | xxxxxxxx | ---------------- |
Snare | --o---o- | --o---o- | --o---o- | oooo------------ |
Fl tom | -------- | -------- | -------- | ------------oooo |
Bass | o---o--- | o---o--- | o---o--- | ---------------- |
Fills come in all shapes and sizes. Drummers will typically mix in quarter bar, half bar and whole bar fills over the course of a single song, but fills spanning multiple bars are not uncommon.