Dead Centre
The position of the working piston and the moving parts which are mechanically connected to it, at the moment when the direction of the piston motion is reserved at either end of the stroke is called the dead centre. There are two dead centers in the engine. They are Top Dead Centre and Bottom Dead Centre.
Top Dead Centre (TDC) : It is the dead centre when the piston is farthest from the crankshaft. It is designated as TDC. It is also called the Inner Dead Centre (IDC).
Bottom Dead Centre (BDC) : It is the dead centre when the piston is nearest to the crankshaft. It is designated as BDC. It is also called the Outer Dead Centre (ODC).