TDC or top dead center is the position of the piston when it forms the smallest volume in the cylinder.
BDC or bottom dead center is the position of the piston when it forms the largest volume in the cylinder.
TDC or top dead center is the position of the piston when it forms the smallest volume in the cylinder.
BDC or bottom dead center is the position of the piston when it forms the largest volume in the cylinder.