吃鸡 literally means "eat chicken" but it's just an expression and here it refers to gaming. Like "eat crow" is an English idiom that makes no sense if translated literally to other languages.
"eat chicken" specifically refers to winning a battle royale. Not sure if it came from PUBG, but this term got really popular in the PUBG era.
To be humiliated or humbled.
Folk etymology: it comes from the poor having to catch and eat crows (which aparently taste disgusting) to prevent starving to death.
_Sort of, it's more anti ghosting, or configuring the keyboards circuit in a way so all of the "gamer keys" don't interfere with each other. Ghosting is when a certain combination of keys are pressed tricks the matrix, activating another key that isnt pressed at all, hence "ghosting".
Membrane keyboards generally only have 2 key rollover (sometimes if 2 specific keys are pressed, none else will register). Some gaming keyboards will rearrange the circuit so that these specific combinations aren't present near WASD. For example on most keyboards, if you press W,A,S, the S key would not register.
Most of the time I just ignore it. I game a lot, and have a big expensive PC and high refresh monitor but I still game on a model M. Membrane keyboard with 2 key rollover, but it's never really affected me honestly.