Wat is Poll-mode driver, user-space network stack?

A poll-mode driver runs in the application’s process: it maps a card’s rings into user space and reads and refills them in a loop on a dedicated core, with no interrupts and no system calls. A user-space network stack implements IP, UDP and TCP in the application’s process on top of such access to the card, usually behind the standard socket calls, so that an unmodified program runs over it.