From the beginning of Christianity special veneration was paid to the Mother of God, which in the language of theology is called hyperdulia, to distinguish the honor rendered to her from that given to the other saints. It is not strange, therefore, that after the main or principal altar, the most prominent is that dedicated in a special manner to the Mother of God; and to indicate this specific preference, this altar is usually placed in the most prominent position in the church, i.e. at the right (gospel) side of the main altar. In general it signifies any altar of which the Blessed Virgin is the titular.
This is a photo from St. Benedict's (Fraternity of Saint Peter) Parish in Chesapeake, VA.