Limited concentration with a measureless object (Buddhism)

Concentration is limited and thus unfit as a condition for a higher jhana; however, the object of concentration is extended and therefore measureless and suitable for a higher jhana.

According to Hinayana Buddhism, concentration is considered as of one kind (monad), of two kinds (dyads), of three kinds (triads), of four kinds (tetrads) or of five kinds (pentad). In the second tetrad, this is the second concentration.