According to System Information, I have about 57 GB of "Backups". What exactly is meant by "backups"? I'm guessing iPad and iPhone backups count, but that only accounts for ~25 GB.
Where is the rest?
These files are stored in /.MobileBackups/ and /.DocumentRevisions-V100/.
I am very surprised that your backup is so large - my Backups are only 300MB!
According to the Time Machine preference pane, TM will "keep local snapshots as space permits". Do you have a lot of spare disk space?
Since these folders are owned by root, to check the size of these folders you'll need to use sudo, or log in as root user. E.g. the command line commands: