What is Open content
Open content is content that is openly accessible, usable, editable, and distributable by anyone for any purpose, even commercially.
Open content is licensed with an open license that authorizes use of the content.
When someone creates something (like a picture or book), they can open it for the use of others. This means that other people are allowed to copy it and change it if they want. The open content may be free of charge, but it does not have to be.
Open Content License
The rules that say how people can use, modify, and share open content is called a license. The license explains exactly what you are allowed to do with the content covered by it. Licenses are often written in complex language (legal jargon), but many licenses contain concise content that is much easier to understand.
The makers of open content get to choose what license to use for their work, and everyone else has to follow it. Only the maker, who owns the copyright, can change it to another license. Most open content licenses say that when others change the work, they must also declare it to be open and under the same license. This is called share-alike and means that anything based on work will always be open content.
All the content in Wikipedia is open under the rules of the Creative Commons Attribution/Share-Alike License, a very well-known open content license. Another well-known open content license is the GNU Free Documentation License.