presure tank?

[Fenvy]

I sold a boost gauge to some guy with supra tt

I was poking around on his card and he mentioned something about stock pressure tank. After furthing inquiry, he revealed that it'll force pressure into your motor when you are low of it.

I don't really know what it means but I suppose something like this could exist and could also be beneficial in terms of performance but my search yields little to no result. Does anyone know what he was refering to and where I can get more info?