频繁 (pín fán) is an adjective meaning 'frequent' — it describes how often something happens (e.g., 频繁的会议 'frequent meetings'). It is more formal and written than the everyday adverbs 经常, 常, 常常, and 时常, which are placed before verbs to mean 'often'. As an adjective, 频繁 can also be used adverbially with 地.