port
termnetworking
A sixteen-bit number that identifies which service or conversation on a host a packet belongs to.
Ports exist because an address identifies a machine and not a program. The number is a label, not a permission: a service is not safer on a non-standard port, and a port that answers is not evidence of what is listening. Two operational consequences follow - sixteen bits means about sixty-five thousand simultaneous conversations per address pair, which is what exhausts under heavy proxying, and any filter written by port number is describing an expectation rather than a fact.
Also known as: tcp port, udp port