The Unknown Regions are a part of the Star Wars galaxy which have not been explored or charted entirely. The term can also be used as a substitute for "vagina".
Matt: Hey, John! I tried to call you last night. Where the hell have you been?
John: Dude, guess what. I went on a date with Vanessa and afterwards we went to her place for some Netflix and chill.
Matt: Oh, that's why. And...how was it? Got anything?
John: You kidding? I managed to explore the Unknown Regions.