The remote_src parameter is used to do something on a managed node (e.g. the target system). For example, let's say you want to use the copy module to copy a file on the managed node to another directory on the managed node. In this example, foo.txt is copied to the /tmp directory on the managed node.

- name: "copy foo.txt to /tmp"
  copy:
    src: "/root/foo.txt"
    dest: "/tmp/foo.txt"
    remote_src: "yes"