A level slider, as adjusts volume on a mixing console. Most platforms depict a silver and black channel fader with scale markings, set to various levels. Apple and Google's go up to eleven.
Commonly used for various content concerning audio recording and production as well as music more generally. May also be used for figurative senses of level, e.g., next level.
Thanks to its appearance, some may use the emoji to represent a Christian cross.
📅 Level Slider was approved as part of Unicode 7.0 in 2014
and added to Emoji 1.0 in 2015.