Things that are purpously made to work the best and is commonly known. Bit like how people know gravity... Is meta. (But it is called Meta because it is a game you are playing. Using stuff that is definetly not your own is Meta.) In Dnd campaigns, playing by stuff your character shouldnt know is Meta. In video games, if you play by the usual and purposfully thing to work. Its meta. There are lots of builds you can call meta, but usualy the most popular ones are the most defined as Meta.
My double Hades + heavy flak spire example is actually a Meta to the builds effeciency.
What makes it non Meta is having AI. It is more effective with AI, but unusual.
Here is another build.
Pyra: Double Merc front, Gat Mort Left. (Aproach with Double Merc, brawl with Left side.)
It has Meta workings on its pair of guns. BUT its placement is unusual.
(Now, pyramidions is the ship that you can be least flexible with in terms of builds so pyras usualy have Meta working weapons)