2016 corpus christi procession benediction at the altar of our lady of guadalupe
In a Roman Catholic church, after the main or principal altar, the most prominent is that the altar of Our Lady.
It is dedicated in a special manner to the Blessed Virgin Mary, Mother of God. 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.
References
Altar of Our Lady Wikipedia(Text) CC BY-SA