When you lubricate something, you make it a little bit greasy so it can easily move or slide. You might need to lubricate a rusted bolt in order to unscrew it, for example.
Mechanics who work on cars need to lubricate engine parts all the time, to remove old ones and attach new ones. Oil is commonly used to lubricate metal surfaces so they don't stick against each other. All different kinds of machines and engines — from jumbo jets to sewing machines — need to be lubricated in order to work properly. The Latin root word is lubricatus, "to make slippery or smooth," from lubricus, or "slippery."