To see something, and have it in your brain, but not completely registered yet...hard to explain if you haven't had it happen to you. Often people who have had it happen to them try to explain it to others with the phrase "Well I knew it, but I didn't KNOW it." The word refers to the period between knowing it and...KNOWING it.
Bob: "I saw that there was no soap in the shower before I got in, but it wasn't until after I was taking a shower that I realized 'CRAP! There's no soap in here!'"
Joe: "Haha, man! You knew it point five!"
Bob: "Yeah, yeah, 'know point five...'"