OFA is the Orthopedic Foundation for Animals, although they have branced out from strictly orthopedics. They certify for hip and elbow dysplasia, thyroid function, and heart function. Their website is www.offa.org
and you will find lots more details on what they do there.
I would not at all consider this health tested. This is vet-checked, which is not the same thing. Health tested means that screening has been done by a board-certified veterinary cardiologist for aortic stenosis and familial ventricular arrythmia, that a full thyroid panel has been run and sent out to one of only six labs in the US that can do the full panel (those labs are listed on the OFA site), that the dog has had their hips x-rayed and either sent in to the OFA for analysis or had a PennHip reading done. If they had them "checked" for hip dysplasia but do not have them OFA certified, they did not have them checked for hip dysplasia - they just had the vet look at the x-ray (if they even had one done) and give his opinion on the status of the hips. If you x-ray a dog for OFA certification, three different vets who are very experienced in reading x-rays and determining status of hips are shown the films before a final diagnosis is made.
Please visit www.boxerworld.com/breeders
for more information on the specific health tests that should be done on breeding stock, and a listing of breeders who perform this testing and have agreed to supply hard-copy results.