The meat and potatoes of WiFi. Essentially everything transmitted by a wireless NIC comes in the form of a frame. They are the basic unit of most digital transmissions, and surround or encapsulate packets.
A typical WiFi frame is broken up into several sections, consisting of a MAC header, payload and frame check sequence.
The MAC header contains a Frame Control Field which includes, among other things, the 802.11 protocol version and frame type. Address fields including the BSSID, source and destination are also part of this section.
The Payload or frame body contains the actual information (typically a data packet) of either a management or data frame.
The Frame Check Sequence (FCS) concludes the frame with a cyclic redundancy check (CRC) sum of the MAC header and payload. This is used to verify the integrity of the frame and is essential to fault tolerance.