what is namespace in docker hub api reference?

Question

I see here a required field 'namespace': https://docs.docker.com/docker-hub/api/latest/#tag/repositories

But what is it?

I tried to find more information in the API documentation, but was unsuccessful.

This request works without 'namespace' curl -s -H "Authorization: JWT $DOCKER_PASSWORD" "$DOCKER_REGISTRY/v2/repositories/$DOCKER_REPOSITORY/tags?ordering=-last_updated&page_size=1"