A lease lets you use equipment without buying it outright. You make fixed payments for the term, and at the end you return the equipment, renew the lease or buy it on the terms the lease sets out.
The purchase option decides what the lease really is. A fair market value lease works like a rental, with lower payments and the choice to buy at a market price at the end. A $1 buyout lease works like a purchase in installments, with higher payments and ownership for a nominal amount.
Leases can be easier to approve and may cover soft costs such as delivery and installation. How a lease is treated on your books and taxes depends on its terms, so ask your accountant before you choose.