Just recently, James Gunn revealed the DCU's definition for metahuman, writing on @Threads:
"In DC Comics, a metahuman is a human-like being with extraordinary, often paranormal, abilities. These powers can arise from a variety of sources, including science, magic, alien origins, mutation, divinity, proficiency, or technology." Therefore 4 (Superman's robot) is probably not a metahuman but Terrific arguably is. Krypto is meta but I won't say he's not human because he might read this."
In the DC Comics continuity, a "metahuman" specifically refers to a human being who possesses a Meta-Gene. This isn't just any power; it's a genetic mutation, conceptually similar to how mutants are portrayed in the Marvel Universe. For instance, if a regular person gets zapped by lightning, they're dead, whereas someone with a Meta-Gene could potentially develop superpowers.
Regardless, it’s evident that Gunn has carefully considered the concept. By expanding the definition of “metahuman” to include virtually anyone with superhuman abilities, he introduces a fresh perspective that could lead to a variety of compelling scenarios and unexpected narrative twists.
In a recent interview with EW, Gunn revealed that the general public in the DCU is well aware of the existence of metahumans as they've been a known quantity for 300 years.
In this world, humanity has been clued into the existence of metahumans (i.e., super-powered individuals) for 300 years, Gunn reveals. ("If you saw a shark-man walking down the street, you'd probably vomit and s--- yourself to death," he says. "If they saw one, it would be more like if you saw Paul McCartney on the sidewalk in New York.")
In other words, metahumans are practically celebrities in the DCU.
Also in EW, Gunn commented on the fact that he's introducing audiences to a world that's already full of metahumans.
Said Gunn, "I grew up reading DC and Marvel comics and having worlds and universes of superheroes who were interacting. I grew up watching Super Friends on Saturday mornings. It's a long time coming, to be able to be a part of a world in which superheroes are real. We don't have to explain everyone away. There's a little bit of magic in this world. There's science beyond our understanding in this world. This is the kind of place where there's an island full of dinosaurs that probably exists."
Now that a Wonder Woman film is officially in development within the DCU, it raises intriguing questions about how deeply this fictional universe of metahumans will be explored. As the franchise expands, it will be fascinating to see how richly its characters, mythology, and world-building evolve.