I think the NetBSD project put the reasoning for this term quite well:
If something looks like a duck, walks like a duck, and quacks like a duck, what is it?
The answer, of course, depends on whether or not the name `duck' is a trademark! If it is, then the closest that something can get, without permission of the owner of the trademark, is `duck-like.'
`UNIX' is a trademark of The Open Group, and NetBSD has not been branded with that trademark. Therefore, NetBSD is not UNIX. We refer to it as `UNIX-like' or `UN*X-like.'
(not to mention if the duck
comes from some of the same code
Update: yerricde points out http://www.unix-systems.org/questions_answers/faq.html, which says:
I for one strongly disagree
with this claim
of trademark abuse
. It's like saying people can't express
something as like another product
. But IANAL