The buses run from 4 a.m. to midnight 'at regular intervals'. [=there is the same amount of time between buses]
It's nothing special, just a 'regular' [='basic'] stereo. = It's just a 'regular old' stereo.
He is one of the store's 'regular customers'. [=customers who shop at the store frequently]
(..) so l thought that's how people lived: riding around in helicopters, learning how to blow shit up. But then, when my mom got busted, I got put in a regular school. The other kids were into Nintendo. Are you ever afraid? No. Not even of dying? No. (..)1991 Terminator 2: Judgment Day