If you see this term online, it usually refers to the of the game, including all balance tweaks, bug fixes, and feature additions released by the developer.
Do yourself a favor: Go to the eShop, buy the game, download the update, and start swinging a pipe at a rival gang member at 150 mph. Your inner 90s kid will thank you.
If you own a legal copy of the game, updating is straightforward. Do not rely on unofficial NSP patches from forum links—they can brick your console or get your account banned.