jQuery projects are released under the terms of the MIT license.
The MIT License is simple and easy to understand and it places almost no restrictions on what you can do with a jQuery project.
You are free to use any jQuery project in any other project (even commercial projects) as long as the copyright header is left intact.
All demos and examples, whether in a code project's repository or displayed on a jQuery site, are released under the terms of CC0.
CC0 is even more permissive than the MIT license, allowing you to use the code in any manner you want, without any copyright headers, notices, or other attribution.
The content on jQuery web sites are released under the terms of the MIT license.
The design, layout, and look-and-feel of jQuery web sites are not licensed for use and may not be used on any site, personal or commercial, without prior written consent from the jQuery Foundation.