Headers and trailers are the concepts of OSI model.

Headers are information structures which identifies the information that follows, such as a block of bytes in communication.

Trailer is the information which occupies several bytes at the end of the block of the data being transmitted.They contain error-checking data which is useful for confirming the accuracy and status of the transmission.

During communication of data the sender appends the header and passes it to the lower layer while the receiver removes header and passes it to upper layer. Headers are added at layer 6,5,4,3 & 2 while Trailer is added at layer 2.