A license is a document that specifies what can and cannot be done with a work. It grants permissions and states restrictions. Broadly speaking, an open license is one that grants permission to access, re-use and redistribute a work with few or no restrictions (definition from Openedefinition.org). There are many open licenses developed for different areas of knowledge. However, when it comes to open educational resources the most typical and common open licenses used are Creative Commons Licenses.
Open Resources are digital materials, such as images, videos, audio, or ebooks which have been licensed for free use. The resource is cited in your works cited page, and you also need to provide correct attribution with the object.
The Format and Elements of Attribution are: Title by Author licensed under CC BY