To have one's cake and eat it too or simply have one's cake and eat it (sometimes eat one's cake and have it too) is the instance of an individual consuming, exhausting, taking advantage of or using up a particular thing and, then, after that thing is gone or no longer reasonably available, still attempting to benefit from or use it. It may also indicate having or wanting more than one can handle or deserve, or trying to have two incompatible things. It is a popular English idiomatic proverb or figure of speech and is most often used negatively. The proverb's meaning is similar to the phrases, "you can't have it both ways" and "you can't have the best of both worlds."
As an example, an individual who is engaged to marry someone but is still dating others romantically would be said to be having one's cake and eating it too.