In the wake of the #metoo movement, light has been thrown on different definitions of rape - clearly the legal fraternity has a different one to the sisterhood of #metoo...
Some very clever metaphors have been used to try and get across the idea of what consent looks like, and my personal favourite is this video illustrating how in the same way you wouldn't force a person to drink the tea they may have asked for, you shouldn't force sex on someone if they don't want it anymore, even if they did ask for it earlier.
Consent is such an apparently difficult idea because until now, absence of refusal was taken as meaning consent - i.e. if you don't say no, you're really saying yes. In no other area of law does this hold up: if I say "buy this car" and you don't say "no", you still don't have to buy the car - you have to expressly say "yes" in order for a contract to come about.
Somehow though, for a very long time (and without getting into feminist conspiracy theory, I'd guess that laws were mainly made by men, and rape victims were mainly women) it was considered that if you were not saying "no" - you were de facto consenting to sex.
The lawmakers eventually added that you had to be in a state fit to give consent (yes, that had to be added!!) - so no consent was possible if you were say asleep, passed out, or highly intoxicated. Some progress I guess.
It leaves the problem that, when confronted with danger, there are three possible responses dictated by our brains: fight (yes, usually the message gets through that it's not consent), flight (ditto) and freeze. Now, freeze could look to the untrained eye of a horny male like "she's lying there, not fighting back, not saying no, so she's ok with what I'm doing". He would quite possibly be wrong - she could just have gone into a frozen state.
Here comes in the notion of enthusiastic consent. The idea is that, in order to be sure that sex is consensual, both parties participate enthusiastically. You can tell when enthusiasm is present, be it verbal or non-verbal. How easy is it to just stop what you're doing unless the other one is clearly as much into it as you are!
I like to bring up the idea of enthusiastic consent in other areas than sex. It is a good yard stick on what is happening in other types of relationships as well.
For example, if you're suggesting to get married, and you get anything less than an enthusiastic response (after the potential shock), then maybe it's not such a good idea.
Or if you're suggesting a change to an employee or a boss, and you get a lukewarm "maybe" - assume the other one is not on board with the change.
Enthusiastic consent allows to remove any doubt on what is going on, any misunderstanding - which I think is the best outcome for everyone involved; and where sex is concerned, it will actually be something enjoyable *for both parties* which I will make the bold assumption is the idea for most of us in the first place!