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1. A structural member whose prime function is to carry transverse loads, as a joist, girder, rafter, or purlin. The term beam may be modified by an adjective indicating its location; as, for example, an end beam or side beam. See anchor beam, binding beam, breastsummer beam, camber beam, ceiling beam, collar beam, cross beam, dragon beam, floor beam, ground beam, hammer beam, I-beam, laced beam, perimeter beam, summerbeam, tie beam, top beam, wind beam
2. A group of nearly parallel rays of light.