A visual approach is an approach when either part or all of an instrument approach procedure is not completed and the approach is executed with visual reference to the terrain. (JAR-OPS 1.435 (a) (8))
An element of an instrument approach system (e.g. an Instrument Landing System (ILS) localiser) is often used by pilots to assist in alignment for a visual approach.
A visual approach is not permitted when the Runway Visual Range (RVR) is less than 800 metres. (Appendix 1 to JAR-OPS 1.430 (g)).