Open access journals are those that publish articles under Creative Commons licenses. Historically, the publisher of research journals held the copyright for all articles, preventing individuals from freely accessing, copying and redistributing research articles except under specific conditions, like quoting/paraphrasing and citing an article in another article.
Through open access, journal publishers make research articles more widely available to the general public for free, without the restrictions of traditional copyright.
Peer reviewed open access journals in several disciplines.
What if the article I find is not open access or CC licensed?
Research articles that are restricted by copyright can still be used for open projects. You can quote or paraphrase from the article and provide a full citation just as you would if you are writing a research paper. You should limit what you use from a copyrighted article to only substantial quotes, results, or findings. Do not copy images, charts, graphs or substantial paragraphs of text into your project.
See our page on Citation vs. Attribution for more on the difference between reusing openly licensed or open access content with attribution and quoting/paraphrasing copyrighted content with citation.