From Longman Business Dictionary
dot-comdot-com /dɒtˈkɒmdɑːtˈkɑm/ (also dotcom), dot.com noun [countableC] COMPUTING a company that does business using the Internet or provides a service on the InternetMany dotcoms tried to build a global brand before their business model even worked.
—dot-com adjectiveadj [only before a noun]The Nasdaq hit its high in March, 2000, and within a few years most of the dot-com sector was wiped out.