Also sometimes referred to as "critical timing".

The idea behind the rolling count is that between the beats (1-2-3-4...) we can imagine smaller "subcounts" that are typically called "and" and "ah", and associate certain actions with them (see below).

The counting then becomes 1-and-ah-2-and-ah-3-and-ah-4...

The exact timing of "and" and "ah" depends on the music...