What is a basilica?

"Basilica" derived from the Greek, meaning kingly or royal, is a term that historically has both an architectural and a canonical meaning. Originally, the halls of justice of ancient Rome, oblong buildings, with three aisles in which the center aisle was separated from the outside aisles by rows of columns and terminated in an apse, were basilicas, and later the term was applied in architecture to those churches constructed according to that definite floor plan. 
 
Legal and general usage, however, considers the title "basilica" as a great honor which the Pope confers on relatively few "regal" churches around the world, a title which carries with it special Papal and canonical privileges. Special privileges such as indulgences are conferred upon persons who visit a basilica and fulfill the necessary conditions.
 
Basilicas are divided into Major and Minor basilicas. Major basilicas are those that have a direct association with the Supreme Pontiff. They have permanent papal thrones and altars at which only those given permission by the Pope may say Mass. Very few churches carry this distinction. 
 
Minor basilicas are referred to as lesser basilicas. They are distinguished as “regal” houses of God and share in some of the privileges of the Major basilicas, such as the use of the basilican insignia - the pavilion and the bell, a special coat-of-arms, and a distinctive corporate seal.