The word "Imām" denotes a person who stands or walks "in front". For Sunni Islam, the word is commonly used to mean a person who leads the course of prayer in the mosque. It also means the head of a madhhab ("school of thought"). However, from the Shia point of view this is merely the basic understanding of the word in the Arabic language and, for its proper religious usage, the word "Imam" is applicable only to those members of the house of Muhammad designated as infallible by the preceding Imam.
For Sunni Islam, what does the word Imam commonly mean?
a person who leads the course of prayer in the mosque