Generally, full backups create at least one additional copy of all data files on a drive, machine, or server during a single backup process. The duplicated files are designated by the user (backup administrator). Backup files typically include files used by applications, metadata to make files more accessible to apps, tracking files to document app processes, logs, and some other control and management files.
However, full backups primarily don't include applications, operating systems, or additional software. Usually, such objects are better copied to backup via disk mirroring or disk cloning. That's why full backups are more helpful in protecting static data. For example, if you have a Word document you wish to back up, you can edit it to its final form and copy it to backup easily. Should a data-loss event occur, you can recover the document precisely as it was from the most current backup. You can even back up multiple file versions to restore different ones depending on the scenario.
With applications, the last-backup copy may be helpful for recovery if you're currently not using the app. If the program is active after the backup, it will create additional data with each passing second. So, the last app backup you have in storage will be able to restore the application as far as its last-backup state. Any data changed after backup completion will be lost following recovery. You can avoid such a scenario if you issue incremental backups to complement the full application backup at more frequent intervals (e.g., 10, 5, 1 minute), so you'll have a current app version in storage at all times.