For Saxon Mullins, there are two crucial words we must all be spreading.

On Monday, ABC’s Four Corners introduced the nation to a brave young woman called Saxon Mullins.

We all knew her story.

She was, as she says, “that girl”. The then 18-year-old who, almost exactly five years ago, was led to an alleyway behind a Kings Cross nightclub and was anally penetrated by a 21-year-old man named Luke Lazarus she’d met four minutes earlier. It was her first ever sexual experience, and the encounter catapulted her into the centre of a highly-publicised rape trial. But never before had we seen her face or known her name.

When the case first went to trial in 2015, Lazarus was found guilty of sexual intercourse without consent by a jury and sentenced to five years jail. But he was out of prison on bail within 11 months after his legal team appealed the conviction. He was granted a retrial with a judge alone, Robyn Tupman. Lazarus was ultimately acquitted. An attempt to reverse this last year with a second appeal failed in November.

The case threw into question our definition of consent.

In her verdict, Judge Tupman agreed Mullins hadn’t consented to sex, but that it wasn’t enough: Lazarus, Tupman ruled, thought Mullins was consenting.

“She did not take any physical action to move away from the intercourse or attempted intercourse,” Tupman said.

“I stress that I do not accept that the complainant, by her actions, herself meant to consent to sexual intercourse and in her own mind was not consenting to sexual intercourse.

“Whether or not she consented is but one matter. Whether or not the accused knew that she was not consenting is another.”

The verdict was devastating for Mullins. Now, aged 23, she has waived her right to anonymity, delivering her first interview with Four Corners.

In heartbreaking detail, Mullins walked reporter Louise Milligan through her experience, from start to finish. It was excruciating, powerful viewing that left many vowing to stand with Mullins.

But Mullins had one key reason for appearing on the show: to talk about consent, and to put an end to the murky grey area that punctuated her case by promoting the notion of "enthusiastic consent".

"Enthusiastic consent is really easy to determine and I think if you don't think you have that then you're not good to go," Mullins said at the end of her interview.

"All you need to say is, 'Do you want to be here?' And very clearly, 'Do you want to have sex with me?'."

Saxon Mullins says we need to teach people that a simple conversation is all it takes to know that you have #consent. #4Corners pic.twitter.com/ux4N6XnBcU

— 4corners (@4corners) May 7, 2018

Mullins' plea is already working. NSW Attorney-General Mark Speakman has referred the state's consent laws to the Law Reform Commission and cited a "systemic problem" with sexual assault convictions.

"(It's) a concern that someone who has not consented can go through four court cases and not get a final resolution for the complaint," Mr Speakman said on Tuesday.

Mullins can't wind back the clocks. But she is bravely turning her experience into a force for good.

Enthusiastic consent means flipping the conversation of 'no means no' to 'yes means yes'.

S.E. Smith neatly explained how it worked for XOJane in 2015 after California passed 'affirmative consent' legislation to help combat college rape culture:

It feels a bit awkward... to explicitly ask someone "would you like to have sex" and wait for a verbal response, and to keep checking in to make sure that everyone is still having fun. But being clear and direct is how enthusiastic consent works, and it doesn't have to feel stiff and clunky... Affirmative consent isn't something that comes naturally right out of the gate, but it's an important learned sexual behaviour.

There are so many reasons a person might not say 'no': fear, discomfort, intoxication, coercion, simple awkwardness.

And so, Mullins wants every girl, boy, woman and man to learn: only 'yes' means 'yes'.

"If it's not an enthusiastic yes, it's a no. That's it," she said.

"And then, you're committing a crime. Simple as that."

If 2017 was the year of #metoo, make 2018 the year of enthusiastic consent. Do it for Saxon.

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Watch Saxon Mullins' full interview with ABC's Four Corners on iView.

The Mamamia Out Loud team unpack the Luke Lazarus case.