A 3X9 scope would be a fixed power 3X scope with a 9mm objective size. Fixed power scopes and binoculars only list 1 magnification with an X behind it. The last number indicates the size of the front objecitve. For example common binoculars or scopes would be 7X35, 8X40, 10X50, etc.
Variable power optics list the range of power settings with a dash between them and an X at the end. For example, 1-4X, 2-7X, 3-9X.
Most of the time the objective size is is added to the end, 1-4X20, 2-7X32, or 3-9X40, etc.
This is a common mistake and most of the time folks know what you really mean. But there are times when it can be very confusing. They make fixed power 8X32 optics and variable power 8-32X optics.