'Altar to the Lord' in the Bible

Then the angel of the LORD commanded Gad to say to David, that David should go up, and erect an altar to the LORD in the threshing-floor of Ornan the Jebusite.

And David built there an altar to the LORD, and offered burnt-offerings and peace-offerings, and called upon the LORD; and he answered him from heaven by fire upon the altar of burnt-offering.