metadiegetic narrative. A narrative embedded within another narrative and, more particularly, within the primary narrative; a hypodiegetic narrative. The situations and events recounted by Des Grieux in Manon Lescaut are metadiegetic in relation to those recounted by M. de Renoncourt (which are diegetic or intradiegetic). When a metadiegetic narrative functions as a diegetic one (when its metadiegetic status is forgotten, as it were), it is said to be a pseudo-diegetic narrative (the Theaetetus). Genette 1980, 1983. See also diegetic level, embedding.
metalepsis. The intrusion into one diegesis (diegese) of a being from another diegesis; the mingling of two distinct diegetic levels. Should an extradiegetic narrator suddenly enter the world of the situations and events recounted, for instance, a metalepsis obtains. Genette 1980, 1983.
metanarrative. About narrative; describing narrative. A narrative having (a) narrative as (one of) its topic(s) is (a) metanarrative. More specifically, a narrative referring to itself and to those elements by which it is constituted and communicated, a narrative discussing itself, a self-reflexive narrative, is metanarrative. Even more specifically, the passages or units in a narrative that refer explicitly to the codes or subcodes in terms of which the narrative signifies are metanarrative and constitute metanarrative signs. Harmon 1977; Hutcheon 19084; Prince 1982. See also narrative code.

Clearly, I need to dig up my old bong before reading that again.
Thanks, Jeff. I always get those terms mixed up.