Apple - Why do I get different Available/Used spaces with Disk Info and df?

Do you have Time Machine backups turned on? If so, the difference may be due to space used for "local snapshots" (essentially, backups to the local disk when your real backup disk is not available). Local snapshots are automatically deleted when the space is needed for something else (actually, it starts purging them when the volume reaches 80% full), so the Finder treats them as free space. du, on the other hand, sees them as used space (as do Disk Utility and System Information).

To find out if this is what's going on, take a look in System Information: From the Apple Menu, choose "About This Mac", then click "More Info", then select the Storage tab, and look for a light purple ("Backups") band on the usage chart. If it's around 47GB, this is the source of the difference.

If you want to disable this feature, you can use the Terminal command sudo tmutil disablelocal -- but I recommend leaving it enabled, as it does provide some useful protection against accidental deletion/file damage/etc when your real backup is not available.

EDIT: As @chillin pointed out, there's an additional source of confusion: df and the Finder are using different units to report the sizes. df is using Gibibytes (=1,073,741,824 bytes), while the Finder is using Gigabytes (=1,000,000,000 bytes). If the Finder had reported in GiB, it would've said Capacity: 232.96 GiB, Available: 166.41 GiB, Used: 66.55 GiB. So there was actually about 52 GiB used for the local snapshots.

df is using Gi = Gibibytes, and "Get Info" is using GB = Gigabytes.