Vulcan telemarketers?
Yuk yuk yuk. But seriously... In the Boolean sense, an operator (such as AND, OR, XOR, NOT) which produces either True or False as its output per its given inputs.
AND returns True if both of its inputs are True, else it returns False. OR returns True if either or both A or B are True. XOR returns True if and only if either of its inputs are True, but not both. NOT returns the logical inverse of its input.
For example, (A AND 0) is False, (A AND A) is True; (A OR 0) is True, as is (A OR A); (A XOR B) is True iff A is True and B is False, or vice versa; (NOT A) is False if A is True, and True if A is False.
And yeah, there are such beasts as NAND, NOR, and XNOR... they are explained elsewhere in this node.