Protocol data units at OSI layer two (data link layer) are called frames. A frame is composed of a layer two header encapsulating a layer three payload. Some common framing protocols include Ethernet, Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), and Frame Relay.
Note that ATM is a common link-level protocol that does not use frames. ATM instead uses a standard 53 byte cell (5 byte header plus 48 byte payload).