Yeah, a trope is a storytelling tool. One that any storyteller, be it writer, visual artist, game designer, or tabletop GM uses either consciously or otherwise.
Plot narrative tools such as 'Chekov's Gun' (a seemingly mundane tool that becomes extremely useful later on) Plot Armor, internal exposition, and even the Villainous monologue are all tropes
Plot situations and themes (from the love triangle to the Big Bad teaming up with the Heros to Fight the Greater Evil) are all tropes too.
And there are Genre and medium tropes (the bottomless pit of death in videogames is a platforming trope...), as well as tropes *involving the use of other tropes*
And I totally didn't just come out of a night full of TV Tropes (which really aught to change it's name since it covers basically everything now).... Okay I did, send help...