A licence is a permit of use that you, as the holder of the right regarding a work, database or other copyright material, may grant to others. Under the provisions on citation right issued in the Copyright Act, direct citations from a work and references to the author are permitted in the relevant context and in accordance with the academic citation conventions of individual disciplines, as long as the original author and source are also mentioned. However, a licence allows you to grant more extensive re-use rights for open access material or, if required, impose specific conditions to restrict re-use or editing.
The most commonly used open access licence system is called Creative Commons. A CC licence includes a global, irrevocable right to redistribute and edit the material. By imposing additional conditions, authors can restrict these rights as they see fit. The licence can later be made more permissive, but it is usually not possible to make it stricter.