The Custom Variables report shows visitor activity by custom segments you create yourself by modifying the Analytics tracking code.
For example, you might have a form on your website where visitors can supply a professional title such as manager, technical specialist, or marketer. In this case, you can use custom variables to capture their selections, where the selections become dimensions for this particular report and subsequent visits remain classified under the selected segment.
Visit our Developer Guides to learn more about custom variables.
Custom variables aren't available for Universal Analytics. If you're using Universal Analytics, use custom dimensions instead. Learn more about custom dimensions or visit the Custom Dimensions & Metrics feature reference in our Developer Guides for more technical information.