Terms of the Trade: What Is a Beam?
In construction, beams are horizontal support structures used in areas that aren't supported by walls. The supported weight is transferred to surrounding columns, walls, or girders. Typically, you'll find beams running down the center of basements and across large openings like in the photo above. For long spans of space, steel is often the material of choice, but glue laminate beams are also used (layers of lumber stacked and glued) as are built-up beams (built-up layers of lumber, plywood or OSB).
Photo courtesy of vancityhotshots.