Netcode
Netcode is a general term that players use to refer to anything to do with the network. Essentially, slang for ‘the game’s network code.’
Players use it to talk about issues
The most common reason players use netcode is when they’re talking about synchronization issues between the client and server. For example, if a player moves behind a wall on their screen but the server hasn’t registered that yet – the player could still be hit. Many of these issues are actually latency issues.