What is .build-deps for apk add –virtual command?

What is .build-deps in the following command? I can’t find an explanation in the Alpine docs. Is this a file that is predefined? Is see this referenced in many Dockerfiles. RUN apk add –no-cache –virtual .build-deps \ gcc \ freetype-dev \ musl-dev RUN pip install –no-cache-dir <packages_that_require_gcc…> \ RUN apk del .build-deps 2 Answers 2