Presumably you refer to your App Library page - this being accessed from either your last Home Screen, or if configured in iPad settings, from the icon at the far-right of your Dock. The App Library is independent from your own folder structure that you create on your Home Screens - which may, or may not, include all the Apps installed on your iPad.
The App Library lists all the Apps that are installed on your iPad. Within the App Library are multiple automatically curated folders that group your installed Apps by category - including an Other folder within which Apps that do not fit specific categories will reside. Category information used to sort Apps within the App Library is derived from the Apple App Store.
You find information about the App Library and how to use it within the frequently overlooked iPad User Guide - this being a rich source of information about your iPad and iPadOS. Here is a direct link to the section of the Guide that describes the App Library:
Find and use your apps in App Library on iPad - Apple Support
In addition to the automatically curated App Library folders, there is an additional special folder entitled Hidden - which will contain Apps that you have explicitly "hidden" from view. Some Users choose to place Apps that they do not wish to be immediately visible from their Home Screens, or the main App Library, for various reasons including privacy:
Lock or hide an app on iPad - Apple Support