A shortcode is a text command inside square brackets [like this] that is inserted in a post, page, or text widget to tell your site to display certain content there. The content is typically created in a separate interface. A common shortcode that is built in to WordPress is [gallery], which displays selected pictures in the page or post where the shortcode is inserted.

Additional language within the shortcode brackets may further specify what content to display, or how to display it, e.g. [gallery type=”slideshow”].

“Shortcode” is a WordPress-specific term. Some shortcodes are built in to WordPress, while others can be added (to self-hosted WordPress only) using plugins. For example, you might install a slideshow plugin, create a new slideshow in the plugin’s settings, and then place the slideshow in a page, post, or widget by inserting the shortcode where you want the slideshow to appear.

Click here for a list of WordPress.com built-in shortcodes
Click here for a list of self-hosted WordPress built-in shortcodes

Some themes for self-hosted WordPress do not support using shortcodes in a text widget.