Charge is a skill used by several different enemies, including Duriel and Diablo. All types of Claw Vipers and Reanimated Horde also use this skill. When cast, the monster rushes toward adventurers and slams them with their relative weapon.
When charging, the enemies move much faster and hit harder than normal, often adding Knockback as well, but they cannot turn while rushing in, and so can be dodged with a fast enough reaction time.
Sometimes the Reanimated Horde "stick" running in place momentarily and then quickly resume walking normally.