I always want to get pedantic about it.
Star Trek canon: Only the episodes and movies, two of the novels (I forget which two), and parts of one of the animated episodes dealing with Spock’s background.
Star Wars: There’s a hierarchy, here… Movies are at the top, followed by the scripts, radio dramas, and novelisations, then the novels (also called “Official” or the “Expanded Universe”) and sourcebooks, then games and comic books (actually, there’s no word on the comic books, but things in there violate the rest quite haphazardly, so that’s how it typically goes).
And, yes, only absolute nerds care about this. Just crown me King.
Star Trek canon: Only the episodes and movies, two of the novels (I forget which two), and parts of one of the animated episodes dealing with Spock’s background.
The two books are Pathways and Mosaic, Voyager novels by Jeri Taylor, one of the series’ creators. The Animated Series episode was Yesteryear.
Also, if you’re going to be King, can you adopt me as the Crown Prince or somethin’? 
King SPOOFE don’t adopt!
But I CAN give you a lifetime pass to the Royal Salad Bar…
I sneeze in the general direction of your Royal Salad Bar and scoff at your claims as the King of Canon! Prepare for war!
I wonder if Tars Tarkas would adopt me if I helped him win the crown… I have as much chance winning it on my own as a Pakled on a planet full of Vulcans does. . .
But it’s a really good salad bar…
Luckily, SPOOFE’s salad bar is equipped with transphasic neutronium-based sneeze shields.
Pft, it doesn’t even have cottage cheese. A salad bar without cottage cheese is no salad bar at all. And where are the croutons?!
Salad bar, bah!
::Rips dessert bar off of foundations and takes back to table::
Time to make my famous whip cream, sprinkles, and carmel fudge slop dessert!
And the best Monopoly token is the Iron!!!
I blame the Andorians.
Where do Ewoks: Battle for Endor, the Ewoks/Droids cartoons, the newspaper-syndicated Star Wars comic strip, and the ever-popular Star Wars Holiday Special fit into that hierarchy?
… Oh, and that Star Tours full-motion-simulator ride at Disneyland. Where does Star Tours fit in? And how about the decorations and voiceovers you get to see and hear while waiting in line for Star Tours?
SPOOFE and Aesiron: link. 
As the term’s used in relation to most multi-volum/film/episode works set in the same fictional “universe,” it generally means the works (books, movies, etc.) accepted as giving the accurate story, as opposed to fanfic, slashfic, titleholder-sold-out-and-licensed-hack-writers-to-generate-garbage works, and related phenomena.
And don’t forget when Luke, Chewie, and the droids were on the Muppet Show!! When did that happen?
(yeah, yeah, a long time ago…)
At one time I could have sworn reading something offical (The Star Trek Encyclopedia, perhaps) that flat out denied canonical status to Star Trek V. I’ve been told recently though, that it is canon, and not apochraphal, which I think sucks.
What?! You’re denying the Holy Revealed Truth of the Almighty Kirk that God lives in the center of the Milky Way galaxy? Blasphemer!
Shatner’s been quoted that “The Three Stooges” was one of his directorial influences for Star Trek V, enough said.
Besides, that wasn’t God. What would God need with a starship?
It’s a little known but impossible to dispute law of the universe that anything containing Bea Arthur is automatically canon.
Actually, for a second I thought you were talking about “kanon” or “in kanon” (how I’ve originally heard it; it’s spelled a bunch of different ways).
I roleplay on a couple of mucks (yeah, I’m a geek ^^), and the term cannon/kanon/ in kanon means that you’re staying in-character; the muck is based on existing characters from fantasy / scifi / anime, and “in kanon” means that you play according to how the character from the series actually would.
For instance, to roleplay Darth Vader and have him dance around in a little pink tutu would definitely not be “in kanon.”
Re: STV:TFF, I’ve heard both sides of the argument. Since they could never make it to the centre of the galaxy in less than 30 years (if I’m not mistaken) there’s no way that STV could be considered canon.
As far as the novels go, I’ve read somewhere that in addition to the Voyager novels “Pathways” and “Mosaic”, the new Deep Space Nine relaunch novels are considered canon as well (including “The Lives of Dax”, “A Stitch in Time”, “Avatar” books 1 and 2, “Section 31: Abyss”, “Gateways: Demons of Air and Darkness”, “Horn and Ivory” (from Gateways: What Lay Beyond), “Mission: Gamma” books 1-4 (Twilight, This Gray Spirit, Cathedral, and Lesser Evil), “Rising Son”, and the upcoming “Unity”.) If they’re not canon, they definitely should be.