If you do something frequently, you do it repeatedly, again and again. If you frequently visit the cookie jar, you might gain some unwanted pounds.
Doctors and nurses have to wash their hands frequently, many times each day, since they touch various patients and don't want to spread germs. When you're driving in rush hour traffic, you usually find yourself stopping frequently. Things that occur over and over, especially in a relatively short time frame, happen frequently. The adverb frequently comes from the adjective frequent, which originally meant "profuse or ample," from the Latin root frequentem, "crowded or repeated."