What does “EP” (Extreme pressure) mean in the name of a lubricating grease?

The term “EP” refers to extreme pressure, which means the grease is formulated with additives that increase its load carrying capacity.  EP greases are capable of withstanding conditions under which ordinary grease may not provide sufficient performance: heavy applied loads, shock loads, high loads coupled with higher speeds, and vibration.  EP grease is needed for many applications of heavy-duty construction equipment, automotive wheel bearings, mining machines, industrial machines operating under high loads, etc.