Sub weapon
From Inkipedia, the Splatoon wiki
The Sub Weapon is a secondary weapon in Splatoon. They use up considerably more ink than a Main Weapon, and as such, usually serve specialized purposes limited to specific combat situations and are not often used as a main method of inking the environment. The light on the back of the player's ink gauge will light up when they have a sufficient amount of ink to use their Sub Weapon.
Two gear abilities have an effect on Sub Weapon function: the Ink Saver (Sub) ability will reduce the amount of ink consumed by a player's Sub Weapon while the Bomb Range Up ability allows bombs, Point Sensors, and Disruptors to travel farther when thrown.
Gallery
List of Sub Weapons
List of Sub Weapons in Splatoon