Never heard of this? Shame on you. It is a dictionary for god's sake! Come on, surely you must have heard of a dictionary right? Even if you are not a native of the English language, you should have heard of a dictionary. But if not, it is okay. I am telling you now - this is the site to go if you need to understand the meaning of a word or a phrase. Or even if you need to find a related word, you can find it here. They have been around for over 150 years, so what they say you should trust. It is not like Wikipedia where everyone can edit and modify stuff, they are a popular source of language information. If you are keen to learn the English language, you should sign up for their newsletter. They have this  "Word of the day" newsletter where they will explain a certain word. Very useful for busy people like me who seldom have the time to learn new words. I especially like their "slang" section, pretty interesting and useful for bloggers.