What does peace mean?

This isn't a comment on a book, but on a book cover--it's meant not to critique a book (which I haven't read), but to examine a screwed up way of talking about "peace."

Robert Spencer has written a book called Religion of Peace? Why Christianity is and Islam Isn't.

Of course you know that I do believe Christianity is a religion of peace, that peacefulness is imbued in Jesus's message. But looking at history, it is easy to believe that Christianity has in practice not been a religion of peace (see this, this, this, and of course this, and I shouldn't have to verify for you that a lot of Christians in America support America's wars). But let's step aside from this historical examination.

The book cover for Spencer's book includes a brief blurb from Ann Coulter on the front, and a longer blurb from Coulter on the back. The front blurb calls the book "a clarion call to America to wake up and fight back." The back blurb says "This goes a long way toward explaining why liberals never wanted to fight this war in the first place."

So let's be clear here: a book proclaiming Christianity a religion of peace, and condemning Islam as being not a religion of peace, features blurbs on the cover by a pro-war Christian criticizing people who oppose a particular war.

So what on earth does "peace" really mean?