Original: No. 1 fuel oil, No. 2 fuel oil and No. 3 fuel oil are  variously referred to as distillate fuel oils, diesel fuel oils, light fuel oils, gasoil or just distillate.
Simplified: No. 1 fuel oil, No. 2 fuel oil (heating oil), and No. 3 fuel oil are referred to as distillate fuel oils, diesel fuel oils, light fuel oils, gasoil or just distillate.