What do you call this side to side selector?

Code pen: https://codepen.io/kiwideejay/full/LzgBGQ/

It's essentially a radio button group - user must have one selected, and only one selected.

The context it's used for isn't really filling in forms - but selected different modes within an app.

As an aside - what's the best way to search these questions? I don't know what words to use.