The Meibomian glands (or tarsal glands) are sebaceous glands at the rim of the eyelids, responsible for the supply of meibum, an oily substance that prevents evaporation of the eye's tear film. They prevent tear spillage onto the cheek, trapping tears between the oiled edge and eyeball, and make the closed lids airtight. There are approximately 50 glands on the upper eyelids and 25 glands on the lower eyelids. The glands are named after Heinrich Meibom (1638–1700), a German physician (source: Wikipedia).
The LipiFlow Thermal Pulsation System uses heat and pressure to open blockages of the eyelid (Meibomian) glands. The treatment was approved by the FDA in 2011. Here is more information: http://lipiflow.com
Here is a Mayo Clinic video about the procedure: