Electronic Library EL Electronic library is a very old term, at least some 20 years of age, I guess. The Virtual Library concept is a subject-oriented link collection based on HTML pages or some database and has been followed by many thousands contributors.
Virtual catalogues are meta-catalogues serching several online catalogues at a time.
In other environments, 'virtual' and 'virtually' unfortunately have a bunch of very divergent meanings. Digital Library Definitions of digital libraries have been discussed several times here, cf the ps list below. Digital Library DL seems to me to be the term best fit and most unambiguous to cover all sorts of librarians' efforts to offer access to digital publications. IMHO 'digital library' and 'digital services' serve this purpose best in our times. Here are some quotations from earlier discussions about digital libraries as compiled from Terry Kuny's digest on the diglib archive, dated 10 Dec 1998 and Bernadette Daly's 15 Dec 1998.