Compression Ratio
This is the ratio between the total volume of the engine cylinder - the place where the piston touches the lowest point in the engine cylinder (Bottom Dead Centre)- to the highest point which the piston touches in the cylinder (Top Dead Center), during the compression stroke. If the compression ratio of an engine is 10:1 , it means the volume of a cylinder is ten times the area in which the air fuel mixture is compressed - the TDC.