Boost

A boost is a benefactor in increasing movement speed either vertically or horizontally.

Horizontal boosts
Explained here.

Vertical boosts
This is just a draft btw: A vertical boost is the act of chaining multiple jumps together to ascend off of MJSG (Must Jump Spam-Geometry). MJSG refers to geometry that the player is unable to stand on normally. They can only hover at, or ascend past, this geometry by continuously jumping in rapid succession.