Time Machine local snapshots
macOS removes these by itself when it needs space, so you usually don't need to do anything.
Between backups, Time Machine keeps snapshots on your Mac so you can restore recent files even when your backup disk isn't connected. macOS deletes them by itself, oldest first, when it needs the space, so you usually don't need to do anything.
Cachet shows how many local snapshots there are. To change how Time Machine works, click Open Time Machine Settings on Cachet's Time Machine page.