That's actually a widely accepted definition of "weak types": automatic type coercion. That said, "weakly typed" is not a well-defined term and I prefer not to use it.
Note that it is not the same as dynamic types. A dynamic type system is a well-defined concept and says nothing about type coercion.
Note that it is not the same as dynamic types. A dynamic type system is a well-defined concept and says nothing about type coercion.