What does ‘interrogative’ mean?

‘Interrogative’ is an adjective that means ‘used in a question’ or ‘having the form of a question’.

Interrogative words (sometimes simply called ‘interrogatives’) are words used to introduce questions: interrogative pronouns such as ‘who’, interrogative adverbs such as ‘why’, and interrogative determiners such as ‘which’.

‘Interrogative sentence’ is another way of saying ‘question’: a sentence ending in a question mark that functions as a request for information.