In gaming, a surboss is a boss battle fought after a main boss, as distinct from a superboss which is, as a rule, vastly tougher and more powerful than a regular boss and may stand alone, like a regular boss, and contrasting with a subboss that is fought BEFORE a main boss.
Tenkai and Matabe, both of Sengoku Basara, are surbosses.
by Bogan of the Desert November 13, 2019