Alphonse Chapanis [EB note: I'm not sure of his exact title; he's a retired professor of HFE at Johns Hopkins University; anyone know?] stated it well in an article in the November 1991 issue of the Human Factors Society Bulletin:
"Human Factors is a body of knowledge about human limitations, human abilities, and other human characteristics that are relevant to design."
"Human Factors Engineering is the application of human factors information to the design of tools, machines, systems, tasks, jobs, and environments for safe, comfortable, and effective human use."
The newsgroup comp.human-factors focuses on the discovery and application of human factors information to the design of systems, software, hardware, and environments related to the use of computers.
[EB note: The society was still called HFS then, so I think the reference should retain that name.]
Human-Computer Interaction, broadly speaking, addresses any interaction with computers by humans, as developers or as users, as individuals or as groups.
"Human-computer interaction is a discipline concerned with the design,
evaluation and implementation of interactive computing systems for
human use and with the study of major phenomena surrounding them."
ACM SIGCHI Curricula for Human-Computer Interaction, 1992, p. 5