Alt, in Latin, referred to height, preserved in our "altitude;" this root appeared in altare, literally meaning a "high place."
In primitive religion it was a common practice to make sacrifices, or conduct worship, on the top of a hill, or high platform, so that "altar" came to be applied to any stone, post, platform, or other elevation used for such purposes. In. the Lodge the altar is the most holy place.
- Source: 100 Words in Masonry
The place where the sacred offerings were presented to God.
The proper form of the altar should be a cube about three feet in height, and having placed upon it the open Bible, Square and Compasses, while around it in triangular form are placed the three lesser lights.
- Source: Pocket Lexicon of Freemasonry