See
http://en.wikipedia.org/wiki/Habeas_corpus
Basically, it means that when you get thrown in jail, that you have the right to appear before a judge to have the judge decide if you deserve to be in jail.
It's a basic right guaranteed in the US Constitution. But, the US Constitution says, "The privilege of the Writ of Habeas Corpus shall not be suspended, unless when in Cases of Rebellion or Invasion the public Safety may require it." (Article 1, Section 9)
Since the US is under no "Rebellion or Invasion," then what the Congress and Bush have done is unconstitutional.
So, if Bush decides (or one of his underlings decides, and then gets Bush to agree) that you somehow assisted a terrorist (maybe your name appears on a mailing list of a group that sent $$$ to a Palestinian charity group that turned out to be run by Hamas), then he can have you thrown in jail. And Bush can deny you the right of Habeas Corpus, the right to appear before a judge to see if you belong there.
Problem is, that if Bush or one of his underlings has a grudge against you, or if you wrote an editorial that they considered to be anti-Bush and pro-Hamas, then they can put you in jail. And they can keep you there without the right to appear before a judge.
Or, if they don't like you, for whatever reason, they can do the same thing. No Habeas Corpus.
Or, if they just make a big mistake, if you look just like someone else who did or said something improper, and they put you in jail by mistake, well, you don't get the chance to appear before a judge and explain things. And you could end up in prison for a very long time.
Not good . . . Not good at all . . .
-Tock