Laminated Structural Timber, also called Laminated Veneer Lumber (LVL), and even called Microlaminated Lumber, is composed of layers of wood joined with glue. It is usually stronger than the same dimension of solid lumber. It costs a little more per board foot, but you tend to need smaller members, and it tends to be very straight and consistent over the entire length of the board. It can be exposed and finished just like solid wood, even with a stain, and it looks nice. A large beam of solid wood would actually cost a lot more than LVL because it comes from a large tree which, these days, is rare. If you are building a post and beam structure, it is a pleasure to work with, again, because it is seldom warped or marred and drills and cuts clean with a sharp bit or blade. The glue does tend to dull blades rather early, but its worth it. It is not always a better choice than steel or a truss joist system, or even a chorded truss. But it is used a lot by an architect for beams and headers.