A sidebar is an area in which it is possible to insert widgets. It can also be called a widget area.

As a rule, it is located in the right-hand column. However, some themes may offer several sidebars. For example, in the left column, where it is also possible to have one on each side of the main content.

A sidebar can also be found under the main content, above it, or in the header or footer areas. In these cases, the sidebar is in a horizontal format, contrary to what its name indicates.

Sidebars play an important role in the layout design of a WordPress site. To customize them, go to the menu Appearance > Widgets.

To learn more about widgets, you can check out The Complete Guide to WordPress widgets.