Refurbished ...

The computer that is shipped by the manufacturer but returned after it is being used for some reason ... may be defective or returned. The manufacturers cannot sell it as new any more ... so they call them Refurbished (after they fix the problem) and sell them to you at cheaper price. They usually carry manufacturer's warranty and can extend the warranty with fee.

Use ...

It is a used computer. Some companies buys them and make sure they run and sell them. They should be called USED but often they are labeled as Refurbished. It may have very short warranty by the seller and cannot purchase any exploded warranty at least not from the manufacturers.

My recommendation ... Manufacturers Refurbished computer are great. I recommend you buy them. Companies like Apple and Dell have great deals on their refurbished computers. Do not buy Refurbished computers from any resellers as they were (1) Used (lease return).