This kind of unofficial branding makes sense, as DC Extended Universe does indeed sound like an official name and has the kind of easy acronym to refer to in casual conversation.
Based on the Marvel Cinematic Universe moniker that has been officially used by that production house, the term DC Extended Universe has been adopted by fans to refer to the films containing crossover of Batman, Superman, Wonder Woman, and many more popular supeheroes.
In a tidbit of interesting studio insight, an online entertainment reporter has discovered that Warner Brothers’ superhero cinematic universe is not officially known as the DC Extended Universe over at production headquarters.
When referring to films like Batman V Superman: Dawn of Justice, Suicide Squad, and Justice League, fans have been saying that these films belong to an intersecting group known as the DC Extended Universe for years.