The word imam denotes the one who stands or walks in front. He is the guide. It is commonly used to mean the person who 'guides' the course of prayer in the mosque; in many cases it means the head of a school. From the Shi'i point of view, this is merely a metaphorical usage of the word. Properly and strictly speaking, the term is applicable only to those members of the House of the Prophet (ahl al-bayt) designated as the infallible.