A fork of Rural Dictionary
A metahuman is someone exposed to some mutagenic compound, such as in the form of a gas, that mutates them down to their DNA, either giving them a superpower or altering their appearance drastically.
See, also, Bang Baby
Bang Baby (a metahuman created by the metagas created by Alva Industries)
Badass Normals, especially ones with low-key superpowers
Robin from Teen Titans 2003 is a Borderline Metahuman