Does it have to be explicitly a meta-mechanic? As in, do in-fiction actions that influence the narrative ()essentially, all of them -- that's kind of the point of play) not count by definition?A narrative mechanics is some resource or ability a player can use to influence the narrative in play. Narrative as in describing a scene and result beyond pass fail state of the character itself. In games such as D&D, these are very rare, in other games they are common and expected part of play.
Most simply, an in-play* mechanism where the player gets to define or alter the wider world, happenstance, or situation in which their character finds them self, rather than the actions or internal reactions their character takes. *at least I think so. If a Player takes an organizational tie for their character during character creation and thus gets to help define an organization that exists in the game world, that is at least a distinct type of situation, although it might be another flavor of narrative mechanic.In your own words, not using jargon or other bespoke terminology. What, to you, qualifies as a "narrative mechanic"?
I think the distinction of calling it a narrative mechanic is necessary. For example, picking a lock or not obviously does influence the narrative in the most basic sense. Allowing the player to narrate picking the lock and everything around and beyond the PC is typically reserved for the GM.Does it have to be explicitly a meta-mechanic? As in, do in-fiction actions that influence the narrative ()essentially, all of them -- that's kind of the point of play) not count by definition?
In games such as D&D, these are very rare, in other games they are common and expected part of play.
I was asked to shy away from jargon, but I suppose trad compared to story now style of RPGs should suffice.Not sure what you mean by "such as D&D". All RPGs? D&D-derived d20 RPGs? "RPGs without Narrative Mechanics"? (That last would be a bit tautological.)
What is/are the key characteristics that define "such as D&D", in the context of this discussion?
Not sure what you mean by "such as D&D". All RPGs? D&D-derived d20 RPGs? "RPGs without Narrative Mechanics"? (That last would be a bit tautological.)
What is/are the key characteristics that define "such as D&D", in the context of this discussion?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.