Basically, in a keyboard several keyswitches share the same wires. Thus when pressing keys on the same wire it can happen that the controller recognize the wron

Basically, in a keyboard several keyswitches share the same wires. Thus when pressing keys on the same wire it can happen that the controller recognize the wrong key or multiple keys. This can be solved and depending on how many keys you can press at the same time it's called 2-key,3-key, etc. or n-key when there is no limit. Should be noted that USB is limited by design to 6-key, only PS2 allows AFAIK true n-key. You can look up matrix-wiring and diodes in keyboards if you want a more realistic explenation regarding the problems in keyboard-design