Maximum Transmission Unit

largest size of a data packet or frame that can be sent in one complete unit over a packet-based computer network, MTU

In computer networking, the term Maximum Transmission Unit (MTU) refers to the size (in bytes) of the largest packet that a given layer of a communications protocol can pass onwards. MTU parameters usually appear in association with a communications interface (NIC, serial port, etc.). The MTU may be fixed by standards (as is the case with Ethernet) or decided at connect time (as is usually the case with point-to-point serial links). A higher MTU brings higher bandwidth efficiency. However large packets can block up a slow interface for some time, increasing the lag on other packets. For example a 1500 byte packet, the largest allowed by Ethernet at the network layer (and hence most of the Internet), would block up a 14.4k modem for about one second.
See more at Wikipedia.org...

<networking> (MTU) The largest number of bytes of "payload" data a frame can carry, not counting the frame's header and trailer.
A frame is a single unit of transportation on the data link layer. It consists of header data plus data which was passed down from the network layer (e.g. an IP datagram) plus sometimes trailer data.
An Ethernet (V2) frame has a MTU of 1500 bytes but the size of the frame can be up to 1526 bytes (22 byte header, 4 byte CRC trailer).
See also fragmentation.
(2000-10-07)