EMZETT.Transmission
In short: The general process of transporting data from a sender over a medium (cable, radio) to a recipient.
In more detail: Transmission is the umbrella term under which almost all other networking terms can be classified: whether via TCP or UDP, wireless or wired — in the end it’s always about getting bits from A to B reliably (or at least quickly).
In Depth
Every transmission can be characterised along several independent properties: bandwidth (how much data is possible at most per unit of time), latency (how long a single bit takes to get from sender to recipient), reliability (does all data arrive undamaged and in the right order) and direction (simplex — one direction only, like classic radio; half duplex — both directions alternately; full duplex — both directions at the same time, as with modern network connections).
These properties are often in conflict with each other: maximum reliability (as with TCP) costs additional latency through handshakes and acknowledgements; maximum speed (as with UDP) does without these guarantees. Which properties should take priority in a specific transmission depends entirely on the use case — a bank transfer needs reliability, a live video call needs low latency.