  We argue that the Penrose limit of a general string background is a
generalization of the Seiberg-Sen limit describing M(atrix) theory as the DLCQ
of M theory in flat space. The BMN theory of type IIB strings on the maximally
supersymmetric pp-wave background is understood as the exact analogue of the
BFSS M(atrix) theory, namely, a DLCQ of IIB string theory on $AdS_5 \times S^5$
in the limit of infinite longitudinal momentum. This point of view is used to
explain some features of the BMN duality.
