Reference dimensions are the type of dimensions you can create on your own using the Smart Dimension command (when the profile environment is not active: if it is active, most of the dimensions you create using the Smart Dimension command are driving dimensions corresponding to constraints).
The Edit Dimension command doesn't apply to reference dimensions: you can't change any size of your parametric model by modifying the value of a reference dimension.
On the other hand, as reference dimensions have an associativity relation to the entities they refer to, whenever the size of the latter changes, reference dimensions will be updated to their new real value. This is also the reason why they are also called "driven" dimensions.