What are I-joists and where can I find them?

• Chapter 7 of the 2005 NDS says:
  
  7.1.2 The term "prefabricated wood I-joist" refers to a structural member manufactured using sawn or structural composite lumber flanges and wood structural panel webs bonded together with exterior exposure adhesives, forming an "I" cross-sectional shape.
  
  Design procedures and other information provided in the NDS apply only to prefabricated wood I-joists conforming to all pertinent provisions of ASTM D 5055.
  
  For more information on I-joists, contact a manufacturer.