An MMO (Massively Multiplayer Online) mouse is a mouse that typically has a lot of extra buttons on the side, near the thumb. It usually has more buttons than a regular mouse, allowing for more customization and easier access to in-game abilities and commands. This kind of mouse is primarily for use with MMO games or MOBA games. MMO mice also often have adjustable weights and higher precision sensors than regular mice, which can make them more comfortable and accurate for extended periods of gameplay.