DotCom

"DotCom" comes from the convention used for generating URLs: The last four letters of the domain name and URLs of a commercial enterprise are ".com" (that is, ".", pronounced "dot", followed by "com", pronounced, oddly enough, "com"). Such a business, being heavily dependent, if not wholly defined by, its web presence, was colloquially deemed a "dot com business" and, ultimately, just a dot-com.