I feel like the main reason these terms are used interchangeably is because people just maybe don't know the difference, but it's just a pet peeve lol. Sex are the biological parts (penis or vagina) and gender is how someone expresses their sex with reference to social and cultural differences. So there can be person who has a penis who's gender is female. So, there's actually no such thing as a gender reveal lol...just sex reveal:) because a baby can't tell you what their gender is. Is this a pet peeve for anyone else? Lol