The * is the universal selector; it matches any element. So your example will apply the style rule to every element.

Thanks.

OK, now I'm curious. Are there any circumstances where you would legitimately do this? As opposed to, say,
html {blahblah}
and letting everyone else inherit from there. Are we talking size, color, what?

he he, one of those questions where the answer begs the question ;).

Not all properties inherit by default Appendix F. Full property table [w3.org], and not all versions would apply inherit even if explicitly set. Hence the popularity of variations of:
* {
margin:0;
border:0;
}

But as the universal selector is very inefficient I think the real message in the question really is to ask if it is the best way to achieve the desired outcome. Legimate? I guess that depends on the code-complexity/code inefficiency trade-off

edit reason
Clarify