Sodium tellurite is a colorless solid. The tellurite ion can react with water to make sodium hydrogen tellurite, NaHTeO3. It dissolves in water easily. It is a weak oxidizing agent (can be reduced to tellurium) and a weak reducing agent (can be oxidized to tellurates). It is part of the process in making tellurium.
Sodium tellurite is used in making tellurium. It is also used to make electroplated nickel corrosion-resistant. It can also be used to add a bluish coating to steel. It can be used to isolate certain types of bacteria that it is not toxic to.