'Sea of Glass' in the Bible

And a sea of glass was in front of the throne, like crystal. And in the midst of the throne, and around the throne, were four living creatures, full of eyes in front and behind.

And I saw as it were a sea of glass mingled with fire. And those who had gotten the victory over the beast, and over his image, and over his mark, and over the number of his name, stand on the sea of glass, having the harps of God.