"Ternary operator" means "operator that takes three things", like unary and binary operators take one and two things.

In C there is an operator for conditional expressions (an 'if' that you can put inside expressions) and it looks like this condition ? trueBranch : falseBranch. It takes three expressions, so it's a ternary operator.

Except it's the only ternary operator in C (and most languages, if they have one at all), so instead of calling it something like "conditional operator", they just call it "the ternary operator"