Refurb is an abbreviation of refurbish, a word the Oxford English Dictionary dates to 1611.
Definition
Refurbish means to furbish again, or otherwise renew, repolish, replenish or restore.
Electronics
Often times, electronics are sold as refurbished products. In this regard, refurbishing is a restoration process where malfunctioned parts are replaced and aesthetic replenishing might have taken place. It can also refer to returned or open-box items that have not been used but cannot be sold as new.
Antiques
Antiques and artwork can be refurbished or restored so it has a "like new" appearance or is otherwise more appealing. It also refers to the conservation process whereby such valuables are preserved from deterioration.
Cars
Automobiles are often restored, whether it be an aesthetic restoration of the body or interior, or a complete rebuild of the car with replacement of parts. It is the aim of such to restore the vehicle to a "like new" state or to otherwise give it its original appearance.
Repairs
In recent years, the word "refurbish" has expanded in usage and is synonymous with "repair." Hotels, theme parks and other public areas often utilize the word in signage when advertising construction, renovation or remodeling.