What does the 'Bi-Metal' mean when referring to a utility blade?

The bi-metal terminology refers to how the utility blade is constructed. With a bi-metal blade, the edge of the blade is constructed of a high speed steel while the body of the blade is made of spring steel. The two sections are welded together to form a single blade. The advantages of a bi-metal blade is that the hardened edge of the blade stays sharp longer than a standard carbon blade and the spring steel body allows the blade to flex without breaking which is common among carbon body blades.