Meaning: Intentionally having sex with a woman (unprotected) and ejaculating inside her with the intention of getting her pregnant. Hence, getting a woman pregnant to get stuck with that person.
The term is based on the exclamation of the moment of conception, acting oblivious by going "Whoops!" upon ejaculation.
Side Note: Helps if she is pro-life too.
If I came across a girl outside my league, I'd have to give her 'The Big Whoops'. Then she'd be stuck with me whether she likes it or not! I'd be like 'Oh yeah, girl -- Whoops!'