An algebraic structure _________ is called a semigroup.ans.

An algebraic structure is called a semigroup if it satisfies the following two conditions:

1. Closure: The operation is closed. This means that if you take any two elements in the set and perform the operation, the result will still be in the set.

2. Associativity: The operation is associative. This means that for any three elements a, b, and c in the set, the equation (a * b) * c = a * (b * c) holds true.

Here, "*" represents the binary operation of the semigroup.

Please note that a semigroup does not require the existence of an identity element or the existence of inverse elements, which distinguishes it from other algebraic structures like groups.