This is an osteochondral allograft, of a plug of bone and cartilage, but allografts may be of other tissues such as ligament and meniscus.
Allografts in knee surgery
An allograft is in reality a 'transplant' - where a graft is 'harvested' (taken) from one person ('the donor') and put into another person ('the recipient'). In knee surgery, we usually refer to allografts in the context of the menisci or cruciate ligament. In the latter, hamstrings tendon, fascia lata, patellar tendon or achilles tendon may be taken taken from the donor and freezedried to eventually replace a damaged cruciate ligament in the recipient.
(NB. The word is never spelled or pronounced 'allograph' - this is a typo that is often found in Forums.)