The term girder refers to a horizontal support beam in construction that supports smaller beams. Keep in mind that all girders are beams, but not all beams are girders. The difference between the two is mainly in the function and not their size. Girders are the main support system and are built to carry large dynamic and rolling loads, which is why you'll often see them in bridge construction. You can distinguish a girder by its typical l-shaped cross-section and stabilization web.