Why did they name Star Wars episode 1 "The Phantom Menace"?

In contrast to the more self-explanatory titles of the other films, the title, “The Phantom Menace” is ambiguous. It is usually suggested that the title refers to either of the two Sith, or the Sith Order itself. The title could also refer to the origin of Darth Sidious’s name, which is the adjective insidious. The Oxford Dictionary gives the following definition:
Full of wiles or plots; lying in wait or seeking to entrap or ensnare; proceeding or operating secretly or subtly so as not to excite suspicion; sly, treacherous, deceitful, underhand, artful, cunning, crafty, wily. (Of persons and things.)

So the word phantom in the title of Episode I could be referring to the Dark Lord of the Sith and menace to the meaning of the name “Sidious.” Another possible meaning of the title is a subtle indication at the ultimate outcome of the Saga—the birth of Darth Vader.

http://starwars.wikia.com/wiki/Star_Wars_Episode_I:_The_Phantom_Menace

this is not fact but I believe is was because of darth sidious and how he was playing both sides of the table and was being a menace in the dark

why not? its such a cool title….

/sarcasm

It’s easy: the phantom menace was the trade federation’s blockade of Naboo. The blockade was the obvious threat, but it was just a ruse (a phantom menace, if you will) orchestrated by Palpatine so that he could become Chancellor. He was the real threat all along.

@bob: Elegant explanation. I actually had never put that together until just now—I never gave the title a second thought.

as a follow up to bob’s thought, the Jedi were unaware that there were any living sith lords at all. As far as anyone knew, the sith had been eradicated,

bob does have a point so it could be either his or maybe this: phantom means: (something apparently sensed but having no physical reality; “seemed to hear faint phantom bells”; “the amputee’s illusion of a phantom limb”) the jedi have no idea that there are still sith in the galaxy so the *[two] current sith are phantoms and a menace to the jedi so they are “phantom menaces” hence the name “The Phantom Menace”.

*Because an army of sith died in a battle because the sith were spread to thin accross the galaxy, Darth Bain set down a law that the sith will never number more than two at a time, usually a master and an apprentece. But that is probably on of those things made up not by George Lucas but by an expanded universe novel author.