both refer to movie chains (i.e., Loews, AMC Theatres) with movie theatres that screen more than one film at a time, as opposed to single-screen theatres. A multiplex has from 2 up to 16 screens, a megaplex has 16 or more screens; plex is the abbreviation for a multiplex theatre.
A morula (Latin, morus: mulberry) is an early stage embryo consisting of cells (called blastomeres) in a solid ball contained within the zona pellucida.
The solid mass of blastomeres resulting from the early cleavage divisions of the zygote. In oocytes with little yolk, the morula is a spheroid mass of cells; in forms with considerable yolk, the configuration of the morula stage is greatly modified. [Mod. morula. 1. the solid mass of blastomeres formed by cleavage of a zygote.