"Freezing Fog
A suspension of numerous minute water droplets which freezes upon impact with ground or other exposed objects, generally reducing the horizontal visibility at the earth's surface to less than 1 km (5/8th mile)."
Published in: AEA 'Recommendations for De-icing / Anti-icing of Aircraft on the Ground' (19th Edition September 04), JAA ACJ OPS 1.345, CAA AIC 105/2003 and SAE ARP4737 Revision D (this is not the latest revision of the ARP).