Panels
Panels is a module that allows site administrators to create custom page layouts using a drag-and-drop interface. It enables the placement of content within these layouts and can override existing system pages for highly customized site designs. It is primarily used for Drupal 7 and early Drupal 8 sites.
An Overview of Panels
The Panels module allows a site administrator to create customized layouts for multiple uses. At its core it is a drag and drop content manager that lets you visually design a layout and place content within that layout. Integration with other systems allows you to create nodes that use this, landing pages that use this, and even override system pages such as taxonomy and the node page so that you can customize the layout of your site with very fine grained permissions.
Sounds great, right? Read more about the power of panels.
Status of Panels
Panels in Drupal 7
Panels 7.x-3.0 is now at a stable release. We usually release once or twice a year. If you're interested in pushing a patch forward for release, make sure to get it reviewed and RTBC.
Panels is an API in Drupal 8
In order to use panels, you must use an implementing module. Currently, Page Manager and Panelizer implement panels.
All new installs of Drupal 8+ are encouraged to use Layout Builder instead. Panels is mostly for D7 and early D8 sites.