Well, "porn" has a very loose definition and varies country by country. IMO it's either nudity (but remember free the nipple movement when you try to define nudity) and/or sexual act usually involving penetration.

Anyway, anyone dancing in a thong isn't even soft-core pornography in my book. Still morally wrong tho in this context.

The norm is moving. People likely seen more naked then many of there ancestors would have combined. Let alone Solidcenter smut.

Victorian ankle showing -> porn

Female moderator showing the weather to be wet soon -> porn

screen unplugged (censored but still) -> porn