This is a big weekend for Doctor Who fans, with the long-running British science fiction program celebrating its 50th anniversary with The Day of the Doctor special. But if Doctor Who makes you say, "who?," don't worry. We can help with the basics. 

We, ourselves, are Doctor Who newbies, having jumped into the series earlier this year with a little help from some experts. After taking a hiatus at the end of the 1980s—(there was a TV movie that went nowhere in 1996)—the series re-upped in 2005 to introduce itself to a new generation of audiences. So, really, you're not that far behind. And the truth is, it's really not that intimidating.  Many episodes stand alone, so it's not that challenging to just, well, start watching.

It might be as good a time as ever to just watch The Day of the Doctor, which will be broadcast simultaneously on BBC America in the U.S. as it airs in the U.K. on Saturday. (BBC America also has a host of other Doctor Who programming to get you caught up.) That said, if you're planning to watch the anniversary special cold, you might need to know some keywords. Hence, we made you a glossary. 

The Doctor: A Time Lord—read: alien—who travels around in time, helping people and aliens out. Has two hearts. Think of him as part Sherlock Holmes, part Doc Brown. 

The TARDIS: The Doctor's spaceship/time machine. It's name is an acronym for Time and Relative Dimension in Space. Looks like an old fashioned British police box. Is bigger on the inside than it is on the outside. Makes a whirring sound. 

Companion: A person that travels with the Doctor. Often female. Often very attractive. See: Billie Piper, Karen Gillan

Regeneration: When a Doctor gets ill or mortally wounded, he doesn't die, he just regenerates with a new face and personality. Conceived as a simple way to keep the show going and change the lead actor. (Regeneration can also be provoked.) Doctors, can, however, encounter one another throughout time, yielding a good set up for anniversary specials. 

The Tenth Doctor: The tenth regeneration of the Doctor, played by David Tennant. Light-hearted, but wise. Wears a pinstriped suit with Converse sneakers. 

The Eleventh Doctor: The eleventh regeneration of the Doctor played by Matt Smith. Floppy-haired. Can be quite childish. Wears suspenders, a tweed sports coat, and a bow tie, the latter of which he deems cool.  

Fez: A style of hat which the Eleventh Doctor also deems cool. 

Rose Tyler: The companion of the one-season-only Ninth Doctor, and the first companion of the Tenth Doctor. Originally a shop clerk, during her travels with the Tenth Doctor, she became separated from him and stuck in a parallel world. Wearer of heavy eyeliner. Played by Billie Piper. 

Clara Oswald: The current companion of the Eleventh Doctor. The Doctor met her multiple times throughout, well, time as she appeared (and died) in various incarnations. He ultimately figures out what's going on with her. Played by Jenna-Louise Coleman. 

Dalek: The Doctor's legendary enemy, a race of aliens that were genetically modified. They inhabit robotic contraptions, and are purely evil and believe in ridding the word of all other races. Think evil R2-D2s. 

"EXTERMINATE": The Dalek's catchphrase. 

Time War: A war between the Time Lords and the Daleks.

Gallifrey: The Doctor's home planet. Destroyed in the Time War, leading to the Doctor's guilt.

The War Doctor: Played by John Hurt. Is mostly mysterious, but based on the latest mini-episode, appears to have regenerated from the Eighth Doctor. 

Zygons: The Zygons only appeared once before, in a 1975 serial with the Fourth Doctor, but they are back for the 50th anniversary. They are red-skinned humanoids and sort of look like giant zits. 

Sonic Screwdriver: A tool used by the Doctor. Does considerably more than a regular screwdriver.