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]
(..) Thank you. "During the Sassanid period, people were divided into two classes, "the royalty, "the upper class and the normal people." "The regular class." What did they ask you? Whether your dad knew she was pregnant. Forgive us for taking your time. There's nothing to forgive. (..)2011 A Separation