Foreclosure is the weapon of last resort for a Mortgagee (a lender, typically) when the mortgagee (borrower) is unable or unwilling to comply with his obligations. If successful, foreclosure destroys the mortgagor's interest in the land and vests it in the mortgagee (s.88-9 Lpa (1925)). Typically the mortgagee will institute forclosure proceedings and obtain an order offorclosure nisi. This will give the mortgagee a fixed time (usually six months) to settle up; after this the mortgagee can go to court again and obtain a order offoreclosure absolute.
Foreclosure has a devastating effect on the mortgagee, and it is often argued that it should not even be available in modern times.