Mae Ffliw’r Adar yn glefyd firysol hynod heintus sy’n cael effaith ar system anadlol, dreulio ac/neu nerfol nifer o rywogaethau adar.  Mae’n lledaenu o un aderyn i’r llall trwy gysylltiad uniongyrchol â hylifoedd heintus, baw adar, ac esgidiau, dillad ac offer wedi’u heintio.
Avian influenza is a highly contagious viral disease affecting the respiratory, digestive and/or nervous system of many species of birds. It spreads from bird to bird by direct contact with infected body fluids, droppings and contaminated boots, clothing, equipment etc.