The super base is a phenomenon during 3-player against 3-player (3v3) matches, where all Command Centers spawn together. This means all the players all are together at the beginning of a match. Superbases are instances where you and your allies just spawn with your command centres right next to eachother, allowing you to build together bigger and easier so you don't need to worry about having an ally halfway across the map.

Credit to:

☀ DaddyD0unts HeartGoldGabriel


Super base from a birds eye view