'Urgh' is a noise, written down. You make it when something disgusts you — a smell, a taste, a sight, an idea — and you want that feeling to come out before any real words do. It is the sound of your face pulling away from something. Use it for spoiled milk, a hair in your soup, a dirty toilet, a horrible photo, or a piece of news that makes your stomach turn: 'Urgh, this milk has gone off.' It can also cover mild pain or tiredness — the groan you make when the alarm rings — though the disgust use is the main one. Two things to know about how it works. First, it stands alone: it is not a noun or a verb, so you do not put it in the middle of a sentence. Write it with a comma or a full stop after it, at the start. Second, it is informal and mostly written — chat messages, comic strips, novels showing what someone said. In speech people just make the sound, and the sound varies: it is really a growl in the throat, so no spelling is exactly right. That is why you will see 'ugh', 'urgh', 'argh' and 'ergh' all standing for roughly the same noise. 'Ugh' is the most common spelling; 'urgh' is common in British writing, where the 'r' is not really pronounced but stretches the sound out. 'Argh' leans more towards frustration than disgust. All of these are relaxed, friendly, everyday — fine with friends, out of place in an essay or an email to your boss.