I know there's countless resources out there for this kind of thing, but I'd like to get a discussion going here so that I can, once and for all, get myself clear on these techniques. If someone asked me to give an example of a simile, I hope I could do so, but if someone asked me what 'Clear as mud' was, I'd be less assured. From what little I understand it's a simile, but if I was then asked why I didn't consider it an idiom, I couldn't answer. And then there's metaphors, which I believe would be something such as The sun moved across the sky like an orange balloon floating across the water. Yes? No? So for starters I'll ask for some clarity on 'Clear as mud'. Is this an idiom or a simile. And more importantly why?