Measureless concentration with a measureless object (Buddhism)

Concentration is familiar, well developed and capable of being condition for a higher jhana; 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 fourth concentration.