Which term refers to a light-yellow liquid in which red blood cells, white blood cells, and platelets are suspended?

blood or  plasma

The light-yellow liquid in which red blood cells, white blood cells, and platelets are suspended is called blood or plasma. 

Plasma is an often forgotten component of blood though it is the single largest component of human blood. It comprises about 55 percent and contains salts, water,  enzymes, proteins, and antibodies. It plays a  crucial role because it carries these blood components throughout the body as the fluid in which they travel.