The Accel Synchro Summon varies from the normal use of Synchro Summoning. All of the monsters utilised for the summoning have to be one Tuner Synchro Monster and 1 non-Tuner Synchro Monster. Accel Synchro Summoning can be performed even during the opponent's turn. The required Tuner monster is called a Tuner Synchro Monster.
In the anime, it has been implied that in order to perform this type of Synchro Summoning, one must achieve Clear Mind at the time. You also need to have extreme speed (when a character Accel Syncro Summons when going at high speed, they will vanish, and then re-appear behind their opponent along with their Accel Synchro Monster).
Accel Synchro Monsters are still Synchro Monsters.
In the TCG/OCG, Synchro Monsters that have the Tuner sub-Type possess a Quick Effect that allows the controller to Synchro Summon during the opponent's Main Phase, with the exception of Life Stream Dragon. Also, Accel Synchro Summoning is not officially recognised as a game term or summoning method. It is a Synchro Summon that occurs during the opponent's turn. As such, any Synchro Monster can be Synchro Summoned with this method.