What does "Quelle est la date de son anniversaire" mean?

I think it means "What is the date of his/her birthday?"
Is that correct?

Yes. That's correct.

Thank you!!

Yes, you are correct! "Quelle est la date de son anniversaire?" means "What is the date of his/her birthday?" in English. It is a question in French to inquire about someone's birthday. To understand the meaning, we can break down the sentence as follows:

- "Quelle" translates to "What" in English, indicating a question about the date.
- "est" is the third-person singular form of the verb "être" which means "to be."
- "la date" means "the date."
- "de" means "of."
- "son" means "his/her."
- "anniversaire" means "birthday."

So, when combined, the phrase asks for the specific date on which someone's birthday falls.