1. The portion of a packet, preceding the actual data, containing source and destination addresses, error checking and other fields.
2. The part of an electronic mail message or news article that precedes the body of a message and contains, among other things, the sender's name and e-mail address and the date and time the message was sent.
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Nearby terms: HDTV « hdx « Head Disk Assembly « header » Head Normal Form » head normalisation theorem » heads down