WordPress is shipped with a current jQuery version by default. When you update your WordPress core and there’s a new version of the jQuery library that is used in the package, it will be updated, too. But you might have reasons not to update your WordPress core, want to use an outdated version of jQuery, or use the jQuery library hosted on a content distribution network (CDN). Google is hosting jQuery and other libraries publicly that you could use and include in your WordPress theme.
I believe that anybody that was involved in developing website at least once, was wondering how you could give two or more DIV containers the same height. Usually this problem occurs if you cannot or do not want to give those containers their height in absolute pixel values. Obviously, there are different approaches for a column layout to achieve this. One of them being the Faux-Column-Technique that uses a vertically repeated background image.