Open Access Journals (often called "gold" open access) are freely available and full text. Many of them are refereed scholarly and scientific journals. The Directory of Open Access Journals (DOAJ) offers an indexing of OA journals by title and by discipline. Many well known and respected journals are converting or modifying themselves to include OA options and are indexed by well-known research databases.
An article reporting new and original research or findings written by the original researcher.
A scholarly journal publishes authoritative articles by academics or experts in a discipline. The articles usually undergo peer-review, that is they are evaluated by other experts before publication.
For more on the different types of periodicals:
Distinguishing Scholarly from Non-Scholarly Periodicals: A Checklist of Criteria from Cornell University Library
Scholarly Journals vs. Popular Magazines Chart from Duke University Libraries