That's how much of the socks I'm knitting are finished. I always consider that when I turn the heel of a sock - in other words make it so that the part of the sock I'm knitting changes from being vertical to being horizontal - that I'm halfway finished and since it's a pair that translates to a 25% finished project. Really I'm a little more past the halfway point. I've turned the heel and have picked up the heel stitches - in other words attached the back of the heel to the rest of the sock - and am now knitting the gusset decreases - tapering the sock down from being the wide part that goes around your heel to the more slender part that goes around your foot.
By the time this is over you may become quite knowledgeable about the different parts of sock knitting. And if you don't happen to knit socks or even knit at all I can't imagine a more pointless thing to know.
I'll see if I can get a couple pictures of my progress tomorrow.