At least, I think the proper word is interrogatives. But, for example, in proper sentence structure, you would see sentences such as,
Are you still here, Alouicious?
Is there a doctor in the room?
In informal speech, sometimes you can omit the actual questioning word, but still pass it off as a question, so long as it isn't confused for a completely different query.
You still here, Alouicious?
There a doctor in the room?
I know it's probably not sound in terms of grammar, but my concern is, is this considered a rude or uncouth kind of language? Or at least, is it considered far less polite than to use the full sentence?
It also shows up in the case of converting, say, "What the <intensifier> are you doing?" into "The <intensifier> you doing?", but I imagine the politeness of that scenario tends to get clouded by the choice of intensifier.