Introductory Note: From my records, it appears that I wrote this (in a very slightly different version) on January 22, 2011, or before. I probably had intended to extend it. I am just going ahead and posting it “as is.”
When a book-collector says “first edition,” he or she is (normally) referring to the “first printing.” However, according to typical “bibliographical” usage, the term “first edition” refers to all those books printed from the first setting of type, and even from plates made from that first setting of type, even if there are relatively minor changes along the way. (Thus, according to a bibliographer, you could easily find books in the first edition printed a hundred years after the first printing.) There are nuances to these definitions, but even if I were to deal with the basic nuances here, there are still unusual circumstances that can crop up and wreak havoc on the definitions. But the basic meanings should be clear.
With certain exceptions, I am not too concerned about the “bibliographer’s definition” of “edition.” As John Carter says in ABC for Book Collectors, collectors have used terms “from the language of bibliography” and certain other fields. But he says that collectors and booksellers “have often given their own glosses and specialised connotations” to such borrowed terms.
I am not at all certain whether the term “edition” originated among collectors (or booksellers), or among bibliographers, or among printers (seems the most likely to me), or among none of those. To me, the specified fields are of equal dignity, regardless of their relative antiquity or lack thereof, and it seems that none should bow to any of the others in terms of which usages might be considered correct.
This is particularly so in view of the fact that many book-collectors are themselves bibliographers, and such people should be in a unique position to choose which word to use in which context. I suspect that most “author bibliographies” have been compiled by book-collectors. This was certainly the case in what is one of the most widely praised and instructive bibliographies, namely Michael Sadleir’s Trollope: A Bibliography.