1 The part of a peripheral mechanism that is in contact with the medium or very close to it and that is directly responsible for writing data or patterns onto the medium or for reading or erasing them. The word is most frequently used of a magnetic head in a disk drive or tape transport (see magnetic tape), an optical head in an optical storage device, or a print head in a printer. See also read/write head.
2 (head-end) One end of a transmission medium. The head has some form of control over the contents of the medium and of access to it. See also broadband coaxial systems.
3 (header) The part of a cell or packet that contains routing and control information used to control the passage of the cell or packet across a packet switching network. See also frame relay, cell relay.
4 The first item in a list.