I thought it was just a more scientific classification.

It’s a classification of sex like biological characteristics, like chromosomes, hormones, and reproductive organs.  Are you asking about that?

Gender is a social construct. Just like race. Where you can be a Black person who is British. Or a Filipino American.

Edit: downvoters, you know you can literally open up a scientific book and verify for yourself, right? Downvotes don’t make a thing false.