Switches are the components that sit under each keycap and register when you press a key. There's a large variety of them that differ in how they feel and sound.
When building custom keyboards, often switches need to be soldered to the PCB. Keyboard builds that don't require soldering switches are referred to as hotswap—installing and changing switches is as easy as inserting them and pulling them out (switch puller required!)
These SP-Star switches are a linear switch, which refers to a smooth switch actuation. They move straight up and down without any tactile "bump" or clicking noise. This is in contrast to a tactile switch which provides tactile feedback in the form of a “bump”, or a clicky switch that has a bump as well as an audible click sound.
Learn more in our Switches 101 article →