Meritocracy (merit, from Latin mereō "earn" and -cracy, from Ancient Greek κράτος kratos "strength, power") is a political philosophy which holds that power should be vested in individuals almost exclusively according to merit.
Advancement in such a system is based on intellectual talent measured through examination and/or demonstrated achievement in the field where it is implemented. 
A difficult question is who decides merit. A meritocracy is likely to degenerate into an elitist system where the rulers govern in their own interest and in the interest of their group. People lower in the meritocratic Hierarchy risk being neglected. Advancement in a meritocratic system is likely to depend at least as much in pleasing existing meritocrats as it depends on ability. If the meritocrats start promoting their less able children and relatives the system can degenerate into an Aristocracy.