Periodically means happening at regular intervals or from time to time. When something occurs periodically, it doesn't happen constantly, but it does happen repeatedly in a pattern you can expect.

A lighthouse beam sweeps around periodically, flashing its warning to ships at predictable intervals, maybe every ten seconds, all night long. Your dentist wants to see you periodically for checkups, probably twice a year. A magazine published periodically might come out weekly, monthly, or quarterly, but always on a schedule readers can count on.

When scientists check on an experiment periodically, they might measure it once an hour or once a day. The key is the regularity: it's not random. Your teacher might review your progress periodically throughout the semester rather than waiting until the end.

Sometimes periodically just means “occasionally” or “now and then,” without implying a strict schedule. You might check your email periodically during the day or clean your room periodically when it gets too messy. The pattern is still there, even if it's less precise than a lighthouse beam.