Months before Derrick Rose took the stand to defend himself in the lawsuit claiming he and two buddies raped an ex-girlfriend while she was intoxicated, the NBA star was asked if he understood the word consent.

“No. But can you tell me?” he asked at a deposition in June.

Rose came to court last week with a much better grasp of the word that is central to the $21 million civil case, though his interpretation of the concept could prove costly.

No one disputes Rose and his friends had sex with the woman in her apartment Aug. 27, 2013. The question is whether she consented — as the men claim — or whether she was too incapacitated to do so — as the ex-girlfiend says.

There is no commonly accepted definition for consent, which is at the heart of a “patchwork quilt” of evolving laws on rape and sexual assault that in some cases require an affirmative agreement before sex, attorney Rebecca O’Connor said.

“It is murky and I think that’s where we’re seeing a lot states try to clear the weeds, if you will, and take this on and make it clear,” said O’Connor, a vice president at the Rape, Abuse & Incest National Network. “It’s so complicated we can never just say it’s black and white.”

Rape was once defined as intercourse with force against a woman’s will, said Matt Lyon, a law professor at Lincoln Memorial University. Reform efforts in some states led to rape being defined more by the non-consent of the victim than a use of force by the perpetrator. States such as California have gone steps further in deciding that consent can be withdrawn during sex and that a victim can be too incapacitated to agree to the act.

“One of the big criticisms against the modernization is the ‘he said, she said,”’ Lyon said. “It’s so easy when it’s clear there was force used, but here the woman may say it was rape though there’s no physical evidence of force or that it was done against her will.”

That is the situation in the Rose case, where the woman said she blacked out and felt drugged after a night of drinking and hanging out at Rose’s Beverly Hills mansion. With no physical evidence, the case hinges as much on her credibility as that of the three men.

The woman said she went home from Rose’s, vomited, and woke up around 3 a.m. to find Rose, Ryan Allen and Randall Hampton having sex with her against her will.

Rose may have been tripped up by the word consent in his videotaped deposition, but he tried to recover at trial by defining it as both parties being in agreement.