When a person (usually a woman) feels no romantic and/or sexual inclination towards another person (usually a man) but still likes him enough to want to know him and spend time with him. So, if you get put in the friend zone, get over the romantic and/or sexual inclination and go with it; it's not such a bad place to be.

It is a sort of mythology, I would say.

A mythology born of male entitlement.

Agree the unreciprocated feelings.
I have female friends, but never think of friendzone with them. Yet ladies, I for all intents and purposes have dated, who want to keep me as a friend only, I think of friendzone.

It's entitlement at its worst. No one owes you anything,particularly not their time or affection. If YOU have feelings for someone,those are YOUR feelings and your responsibility. It has literally nothing to do with the object of your affection and they have absolutely no obligations toward you.

Liking to hang out but no sex

Honestly I define it as whining. (Not to be rude, that's just how I define it)

I think you're on the right track with your definition.

I only came across this description for the first the other day, on here funnily enough. It just sounds like a trendy term that you described in your post but for me has no meaning whatsoever. If I fancied someone who didn't fancy me and they wanted to plonk me in this zone my response would be - yeah whatever.