Netflix and Chill is an invitation to watch something at home that is usually a coded suggestion for a casual hookup.
Netflix and Chill sounds like a relaxed night of streaming, but it became internet slang for inviting someone over with sex as the real intention.
The phrase took off around 2015 as a tongue in cheek euphemism. Asking someone to come watch a movie was rarely just about the movie.
The invitation usually points to something casual rather than a real date, and little actual watching is expected to happen.
Because it is so well known, using it earnestly can come across as a cliche or as assuming too much too soon.
As with anything physical, it only works when both people want the same thing. A shared laugh about the phrase is often the clearest sign you are on the same page.