An altar of Our Lady is a side altar in a Catholic church, usually the most prominent altar after the main or principal altar.
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 a prominent position in the church, to the right of the main altar (the gospel side), or as the focal point of a distinct Lady chapel.
In general it signifies any altar of which the Blessed Virgin is the titular.