I have no idea. You need to provide more context. What was the complete sentence?

Oh, I see. Perhaps Susan can add to this, but in plain English, it is a "chap" or "fellow" or in a slightly different context, it is a kind of fellow who talks a lot about everything, rather like a "Know---It---All". The person may be disliked because he talks, and talks, and talks. So his mouth movements might be similar to a dog wagging his tail constantly, Back--And---Forth. Some of the personalities in the News Media can be referred to as a "wag". In the same sense, they are also referred to as "Talking Heads". It is just some "head" that is there going "Blah, blah, blah". We might use WAG in a sentence like this. "Some wag was going on and on and on about the financial crisis until I just wished he would shut up!" or, "Some wag appeared in a pop-up on my computer going on and on about the best investments and the impending econonmic collapse of the whole world. Good grief! What a nut! Wags like that just hack me off!" (make me angry)

"wag" is something a dog does with its tail when it goes back and forth. "wage" is what money people are paid for their work. Something "imagined" is something that is pictured in the Mind. As Susan indicates, you need to offer more information.