Finishing up the year in the Bible, I heard this passage:
Then I saw thrones, and seated on them were those to whom the authority to judge was committed. Also I saw the souls of those who had been beheaded for the testimony of Jesus and for the word of God, and those who had not worshiped the beast or its image and had not received its mark on their foreheads or their hands. They came to life and reigned with Christ for a thousand years. The rest of the dead did not come to life until the thousand years were ended. This is the first resurrection. Blessed and holy is the one who shares in the first resurrection! Over such the second death has no power, but they will be priests of God and of Christ, and they will reign with him for a thousand years.—Revelation 20:4-6 (ESV)
Surprisingly, this seems to be the only use of "resurrection" in that book. It sounds like there will be one resurrection at the start of the thousand years (of those who had been beheaded and remained faithful) and that everyone else will be resurrected at the end of the thousand years.
On the other hand, the immediate referent of the phrase is "The rest of the dead did not come to life until the thousand years were ended." That would imply that, while the martyrs did come to life and reign with Christ, that event was not properly a "resurrection".
Can we know from the text (and not from any particular doctrine of eschatology) whether there are multiple resurrection events or if there is a distinction between coming [back] to life and a proper resurrection?
To clarify: the Jewish conception of resurrection at the time was that God would bring people back to life once and for all to reward them so they could enjoy life forever. (Most likely, the wicked would be returned to life in order to face justice, but the sources are less clear about them.) The event was to occur just once in all of history in the same way that creation only happened once. The rare cases of people being raised from the dead weren't considered resurrections since there was no judgement and the people would die once again.
Paul also speaks as if there will be just one resurrection:
Behold! I tell you a mystery. We shall not all sleep, but we shall all be changed, in a moment, in the twinkling of an eye, at the last trumpet. For the trumpet will sound, and the dead will be raised imperishable, and we shall be changed.—1st Corinthians 15:51-52 (ESV)
So one way we can interpret the Revelation passage above is to see what happened to the martyrs at the beginning of the thousand years as a simple revival from the dead. The pattern would be the Shunanite child revived by Elisha (as suggested here) or Lazarus.
But the literal reading of the passage is that the martyrs are a sort of first wave of the resurrection. Hence the possible contradiction and the question.