Open Access is . . .
If an article is "Open Access" it means that it can be freely accessed by anyone in the world using an internet connection. This means that the potential readership of Open Access articles is far, far greater than that for articles where the full-text is restricted to subscribers. Evidence shows that making research material Open Access increases the number of readers and significantly increases citations to the article - in some fields increasing citations by 300%.
What Open Access is not
It is important to point out that Open Access does not affect peer-review; articles are peer-reviewed and published in journals in the normal way. There is no suggestion that authors should use repositories instead of journals. Open Access repositories supplement and do not replace journals. Some authors have feared that wider availability will increase plagiarism: in fact, if anything, Open Access serves to reduce plagiarism. When material is freely available the chance that plagiarism is recognised and exposed is that much higher.