What does datagram mean?
A datagram is the basic unit of data transmission in connectionless packet-switched networks such as the internet. Each datagram is a self-contained message that carries within it all the information needed for delivery — most importantly the destination address — so it can travel through the network independently of every other datagram, without any prior arrangement between sender and receiver. This independence has practical consequences: datagrams belonging to the same conversation may follow different routes, arrive out of order, be duplicated, or fail to arrive at all, leaving higher-level protocols to detect and correct such losses. The term is central to the Internet Protocol suite, where "IP datagram" describes the network-layer unit and "UDP datagram" the transport-layer equivalent, and it formally distinguishes this style of communication from connection-oriented approaches that establish a fixed path first. Though rarely heard outside engineering circles, the datagram is arguably the concept on which the modern internet's resilience and scalability rest.
nounA datagram is a self-contained, independent packet of data carried across a packet-switched network, containing sufficient addressing information to be routed from source to destination without any prior connection setup or reliance on other packets. It is the basic transmission unit of connectionless protocols such as UDP and IP.
- A self-contained packet of data transmitted over a packet-switched network without establishing a prior connection, carrying its own source and destination addressing.
"Each datagram travels independently through the network, so packets from the same message may arrive out of order."
"The DNS query was sent as a single UDP datagram."
"Because IP treats every datagram as independent, fragments of a large message can take different paths to reach the host."
Standard regular plural; used freely when discussing multiple packets.
"The firewall dropped several malformed datagrams during the attack."
Every time you stream a video or load a webpage, thousands of tiny self-sufficient messages called datagrams are finding their own way across the internet — no map, no guide, just a destination address on each one.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of datagram
Datagram was coined in the early 1970s by American computer scientists working on early packet-switching research — it is usually credited to the CYCLADES project community, with Louis Pouzin's group popularizing the term around 1972–1973. The word blends "data," from Latin datum ("something given"), with the suffix "-gram," borrowed via telegram and diagram from Greek gramma ("letter, something written"). Its cognates therefore include telegram, diagram, and program, all sharing the Greek root graphein/gramma meaning "to write."
How datagram is actually used
Strictly technical register: used almost exclusively in networking, computer science, and standards documentation. The term is deliberately neutral in connotation. It contrasts implicitly with "virtual circuit" or "stream" models of communication; writers typically reserve "datagram" for connectionless service rather than using it as a loose synonym for "packet."
Easily confused with datagram
"Packet" often refers broadly to any network data chunk (especially at the link layer), while "datagram" specifically denotes an independent, connectionless unit — e.g., a UDP or IP datagram — that carries full addressing and needs no established connection.
A frame is the data unit at the physical/link layer wrapped with hardware addresses, whereas a datagram operates at the network/transport layer before such encapsulation.