If you are searching Finder for "app", the results that get returned may include the multitude of files that have those letters in their filenames. Those may include files such as com.apple.bluetooth.services.cloud or com.apple.watchkitlist. It may also include results that are applications and perhaps even files that have been provided by Apple as the publisher.
If you're looking for something more specific, you'll have to be more specific when you enter you search criteria.
If a file is found on your computer, then it is taking some amount of drive space. This could be as little as a few kilobytes to several megabytes or even gigabytes of drive space.
If you'd like to know more about any of these files, simply click to select one in Finder and then click File > Get Info (or press Command-I). You will be offered information about that file.
Get file, folder, and disk information on Mac - Apple Support