Greek Chorus

I've only read a couple of the ancient Greek plays in my life, and those a long time ago. The only thing that really stands out in my memory is that along with the characters in the play, there was a another part. We referred to it as 'the Greek chorus'. This was played by several people who voiced together what was going on in the play throughout the performance. In their fixed role outside of the acting, they echoed lines, or cast out clarification or judgment.