What dose 40x mean in 40xescape?

I've never heard of escape 40x, but 4X applied to games in general stands for eXplore, eXpand, eXploit and eXterminate. The term was originally coined in a review of Master of Orion, but the Civilization series is also a prime example of the genre.

Generally in a 4X game there are multiple goals that count as victory conditions, so you can choose the one that's most compatible with your play style.