Hieratic scale is "the use of different sizes for powerful or holy figures and for ordinary people to indicate relative importance. The larger a figure, the greater their importance" (bowersarthistory).
For example, in medieval art that depicts scenes from the life of Christ, Christ is usually larger compared to surrounding figures because he is the most important. We also see this in depictions of the Buddha, where he is larger than surrounding boddhisatvas or disciples.
Hieratic scale is sometimes called the hierarchical scale.