COPY in Docker: why does this one contain more that 2 arguments?

  docker, dockerfile

In a docker instruction there’s a command COPY and I’ve come accross this one:

COPY --from=my_dir1 

I expected there to be a source and a destination, but here there’re multiple arguments.

What correspond to what? What does this particular command in my example do?

this doesn’t explain it

Source: Docker Questions