MGD stands for meibomian gland dysfunction. These tiny glands are situated around both eyelids, just under the eyelashes and there are about seventy five of them. The produce a clear, oily liquid called meibum that goes into the tears enabling them to spread and hold the tears in the eye. If they become blocked, inflamed or the liquid is too thick, it cannot be released and the tears evaporate quickly and lead to dry eyes.
This is different to blepharitis as you can treat blepharitis yet still have MGD.