What is the highest point of a piston called?

The highest point of a piston in an engine is referred to as Top Dead Center (TDC). This term specifically denotes the position of the piston when it is at the uppermost point in its cylinder during its cycle. At TDC, the volume within the combustion chamber is at its minimum, which is critical for the combustion process.

Understanding TDC is important because it serves as a reference point for several critical operations within an engine, such as ignition timing and the determination of compression ratios. It marks the point where the piston is poised to begin its downward stroke and where the intake or exhaust valves are positioned in relation to the piston movement.

In contrast, Bottom Dead Center (BDC) refers to the lowest point of the piston, which has different implications for the engine's cycle. The service limit pertains to the maximum wear or the minimum acceptable dimensions in mechanical parts, while piston stroke refers to the distance the piston travels between TDC and BDC. Hence, TDC is the clear answer in the context of the question regarding the highest position of a piston.