1: Software that serves no useful purpose, but impairs the function of your computer, often due to using up RAM. Unlike spyware
this is just due to poor design rather than malicious intent.
2: Software designed to make computers easier for lusers
to use, but ends up teaching them bad habits which cause them to wreck their computer or otherwise make using it more difficult than it needs to be.
Much of the "bonus" software that comes pre-installed with home computers sold by major manufacturers tends to fit one or both definitions of "retardware".