Datagram

A datagram is the smallest independent data unit carrying sufficient information to be routed on its own from a source to a destination computer in the packet-switching model.

URLs:

RFC 1360

The Internet Architecture Board Official Protocol Standards

W3E References:

packet switching

A datagram is an atom in the packet switching model.

Detail:

Under certain circumstances, a datagram originally transmitted as a single unit will arrive at its final destination broken into several fragments. The IP layer at the receiving host must accumulate these fragments until enough have arrived to completely reconstitute the original datagram.