it could mean quite a few things, but blown head gasket is one.
First-A head gasket is located in between the piston cylinder head and the engine block, inside a car engine. Now a blown head is a blown head gasket. It causes the engine to overheating. All the engine parts are made of metal. So, when the temperature of an engine heats beyond a point, it leads to the blowing of the head gasket. The gasket has failed to seal the space between the head and block. This allows coolant to enter the combustion chamber or the oil galleys. It can also mean the head has cracked.
A bad head gasket , warped head , cracked block etc.
Cracked block or blown head gasket.
If by "under" you mean below, the intake gasket may be blown out. If you mean inside the valve cover, you may have cracked block or head or a blown head gasket.
Either a blown head gasket or a cracked block possibly
The head gasket is gone or the block/head is cracked. Water is mixing with oil. If you remove the valve cover and the head or the intake manifold you may notice a fluid of a deep battleship gray color. This is due to grinding metal fillament mixing with the water and lubricant due to failed lubrication because chances are that you are losing oil if the block is cracked and engine coolant is mixing with water and oil or the head gasket, or the manifold seal is broken and may need to be replaced. An oil leak doesn't always mean that the block is cracked-- your problem could just be a broken head or manifold gasket. This is easy enough to replace but requires extensive dismantling of the top of the motor.
I think you mean head "gasket" - not casket. This is the gasket that is placed between the engine block (bottom part of the engine) and the cylinder head. Your Disco has two heads, so two head gaskets, a left one and a right one.
This means that a gasket has been broken that keeps the head separate from the block. The engine will overheat easy or water will flow into the oil compartments in the engine. Either way, this needs to be fixed before the engine is used.
That usually means that you have exhaust gasses dissolved in your radiator coolant; generally indicative of a head gasket problem or a cracked head (or block for that matter).
It will be the only side all the holes line up with the holes on the block. Check it out, you'll see what I mean.
I take it you mean the head gasket. Head gaskets are pretty cheap, but the labor is high. If it is a V 6 or V8 you may have to do only one side. A lot would depend on what engine you have. I don't know if it is a car, boat or what, so it is hard to say what all is involved. You do have to remove the head from the engine to install a head gasket.
You have a failed gasket, seal, or hose.