the technical term is a resonator chamber. i call it the air box because its where the intake sucks in from. you can take it off and it wont make any difference in performance or sound. its used to remove some sound from the intake but it doesnt do much but take up space in the engine compartment. i always take it off on all my hondas and add an extra air filter where it would normally connect to the air box or add a cold air intake.