A little more fancy than the proverbial welcome mat, the red carpet was traditionally used (I don't know when it first origionated) for dignitaries and diplomats arriving somewhere. A strip of red carpet was placed so that people would walk along it to wherever they were going. "Rolling out the red carpet" implies a fancy, no-holds-barred reception for someone or something. Also used in a sarcastic manner; ex: some military aircraft are approaching a target and see some AAA emplacements. One pilot would say to the other, "looks like they rolled out the red carpet for us."