This is a page with right sidebar. A sidebar in WordPress is referred to a widget-ready area used by WordPress themes to display information that is not a part of the main content. It is not always a vertical column on the side. It can be a horizontal rectangle below or above the content area, footer, header, or any where in the theme.

The usage of sidebars varies and depends on the choices of the theme designer. Many WordPress themes support multiple sidebars also known as widget ready areas.
sidebars are a great place to put important information that you want visitors to have quick access to. Depending on the blogging application and theme or template you use for your blog layout, you can customize your blog sidebars to display the same information on every page and post or different information based on different page and post layouts.

The top of a sidebar (particularly the part that can be seen on the top of a visitor’s screen without scrolling, which is referred to as being above the fold) is important real estate. Therefore, this is a good place to put critical information. It’s also a good place to sell ad space if you’re trying to make money from your blog because space above the fold is more coveted than space below the fold simply because more people will see it. The further a visitor has to scroll down a page, the less content published there will be seen simply because people don’t like to scroll.

Therefore, less important information should be placed further down on your sidebar.