Every place I found that explained it did so *really badly*. It's a force over distance! So, say, carrying a plate? No, because the force isn't in the right direction. Oh. Okay. So, what about a weightlifter? Well, that counts as work. It takes a force to lift objects, and you're lifting it towards you. But, er, doesn't it take a force to move the plate forward? NO! That's not work! So, okay, what about a box? Pushing a box. Yes, that's work! Pushing a box at a constant speed is work! Wait, no, it's not. So, is pushing something more slowly less work, or the same amount of work? Or no work?
Finally, after muddling through a badly-explained chapter and a half, they sort of say in passing "Therefore, work is the change in kinetic energy."
Why didn't you say so BEFORE?