N-key rollover means your keyboard can register every key simultaneously, no matter how many you press at once. To test: open an online keyboard test and press as many keys as possible at the same time — all pressed keys should highlight. Start with 3 keys, then try 5, then 8+. A keyboard with 6KRO will register up to 6 simultaneous keys; full NKRO will register all of them. Note that NKRO sometimes only works over USB, not Bluetooth (Bluetooth typically limits to 6KRO due to protocol constraints). If some keys don't register during simultaneous presses, your keyboard has a rollover limit at that number. This matters most for gamers (who press movement + action keys together) and fast typists who frequently overlap keystrokes.