Just one form of finance available to a company to fund the use of Capital Equipment. Containing many tax advantages, and elements of a 'residual value' of the asset making this form of finance quite cheap. The asset is held as security against this obligation to pay a rental.
A funny finance term - but really very simple. Similar to hire purchase - to buy a car, but for companies. You don't own the car until to have made all the payments, but you have use of it in the meantime.