foreclose on (something)
To take possession of a property to satisfy a debt owed (often related to unpaid mortgage payments). Typically done by banks and other such mortgage lending institutions. You know, the bank can foreclose on your house if you don't pay your mortgage.
foreclose on something
to take the property on which a mortgage is held; to satisfy an unpaid loan by taking ownership of the property put up for security on the loan. If you don't pay, we will be forced to foreclose on your house. The bank foreclosed on our property.