There is a distinction between archivers and other compression
programs:

- an archiver takes several input files, compresses them and produces
  a single archive file. Examples are arc, arj, lha, zip, zoo.

- other compression programs create one compressed file for each
  input file. Examples are freeze, yabba, compress, gzip. Such programs
  are often combined with tar to create compressed archives (see
  question 50: "What is this tar compression program?").

For a comparison of zip and gzip, see the gzip README file. (In short:
zip is an archiver, gzip is not; only zip is compatible with pkzip.)

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