What does Slip the clutch mean?
The driver applies or releases pressure on the clutch to move the car a little or to hold the car in one place on a hill. It's called slipping because the clutch plate slips against the flywheel. This is not good for the clutch.
It's the part that connects the engine to the transmission, and is activated by the clutch pedal inside the car. It's a set of metal disks that 'clutch' or grab onto each other to allow some slip between the engine and transmission. This slip is what lets the car start from a dead stop without killing the engine.
What makes a fan clutch fail I fixed a front oil seal leak on my Suzuki Samurai but now I'm thinking that the oil might have made the fan clutch fail...?
It is when the clutch will not hold. Like you can be driving up a hill and you can rev the engine with no increase in road speed. With the park brake set hard, the car should stall if you attempt to drive off. If you have the clutch out in first gear and the engine can still run and the car isn't moving, the clutch is slipping.