DK yarn vs. "Regular" acrylic yarn

So I'm still not good at understanding/knowing what weights yarns are. I just read a review on Amazon.com that said the blocks in 200 Crochet Blocks were designed with DK weight yarn (I don't have a clue what that is!). The same reviewer says that "regular" acrylic weight yarn is bigger and will make an 8" square. Oh, yay! I'm going to start all over again and make them with a 4mm hook and see what size they come out.