'Garage' was a largely American phenomenon in the 1960s (presumably they had more garages per capita). It was 'amateur', guitar based and largely commercially unsuccessful though there was a lot of it, in every garage, so to speak.
It was mainly male, but there were also female groups such as the Pleasure Seekers (featuring a young Suzi Quatro) and The Debutantes, both from Detroit and two of the first all female rock bands, as opposed to 'girl groups' who sang but didn't play the instruments.