Pedantic prescriptivists claim that "alright" is not a word. That it's merely a misspelling of "all right". I disagree. I claim that "alright" is a word with a meaning distinct from "all right".
The distinction is similar to the differences between "already" and "all ready", and "all together" and "altogether". In each case, when "all" is a separate word it means just that, all. If a group of something is all ready, then all the members of that group are ready. As a single word, the "al" doesn't mean anything separate from the rest of the word.
It's the same with "all right" and "alright". "All right" means everything is correct. "Alright" is synonymous with OK.
Here's another blog on the same issue. Oddly, it says that "alright" isn't a word, and then goes on to describe the difference between the two.