Visual meteorological conditions (VMC) are the meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling equal to or better than specified minima. (ICAO Annex 2: Rules of the Air)
VMC are detailed in ICAO Annex 2. Essentially, they are:
When above 3,000ft or 1,000ft above terrain, whichever is higher:
1500m horizontally and 1,000 ft vertically from cloud;
Flight visibility 5km below 10,000ft and 8km above 10,000 ft.
When below 3,000 ft or 1,000 ft above terrain, whichever is higher: