What is a Media Item?
A media item in WordPress is a file that you can embed in a page or post. WordPress supports several media formats out of the box, including popular options such as JPG, JPEG, GIF, and PNG.
More About Media Items
WordPress supports multiple media formats, which means that you can upload different types of files to your site. Recognized media items will appear in the library and you can add them to posts and pages using the WordPress editor.
The WordPress Media Library enables you to browse existing items and select individual entries. You can add metadata to individual media files and, depending on their format, you can also edit them. If you’re working with images, WordPress enables you to resize the files and to edit them using basic options such as cropping.
Keep in mind that WordPress will not enable you to upload media files in formats that it doesn’t support. However, you can add support for additional filetypes using custom code and plugins.