Butch is a gender expression where an individual express on present themselves as masculine. The masculine trait could be physical, mental or emotional. A common misconception is that only lesbians with masculine traits are butch. However, butch is a gender expression and is not assigned to any one gender identity or sexual orientation.
Sources:
https://nonbinary.wiki/wiki/Butch
https://www.mvc.edu/files/Allies_Terminology.pdf
https://gender.fandom.com/wiki/Butch
https://www.them.us/story/inqueery-butch