How about the definition in AACR2R, App.D:  Serial. A publication in any medium
issued in successive parts bearing numeric or chronological designations and
intended to be continued indefinitely.  Serials include periodicals;
newspapers; annuals (reports, yearbooks, etc); the journals, memoirs,
proceedings, transactions, etc., of societies; and numbered monographic series.

Florence Hayes
Cornell University Library
FH3@CORNELLC.BITNET