Pedestal Buttons are a game mechanic used within the Portal series. They can be found very frequently throughout Test Chambers and are primarily used to allow the player to trigger or toggle a particular function. They can be activated with the "Use" key (default: E).
In the bonus maps of Portal: Still Alive, pedestal buttons connected to cube droppers have a special skin, pictured below.
Pedestal Buttons are used for multiple purposes to initiate a particular action. More common uses include the dropping of a Cube (and fizzling of the previous cube if present), activating a Gel pipeline or opening a door. They can also be timer-based, where the action (for example, extending a platform) is only activated for a specific length of time.