Cinepak is a video codec,
originally developed
by Apple and SuperMac Technologies
for playing moves from CD-ROMs,
then later taken over by Radius, Inc,
and is now the trademarked property of
Compression Technologies, Inc.
Cinepak is a codec, not a file format,
and therefore needs to be encapsulated
in some kind of format. Both the AVI and
QuickTime file formats can support
Cinepak-compressed movie clips.
The Cinepak codec targets movies
of medium-to-high bitrates
with quite good quality, but
(in my experience) performs
suboptimal on low bandwidths
(such as dial-up connections).