There is a distinction between sherbet and sorbet.
Sorbet is made with two ingredients typically (not required to be only two, though): ice (non-negotiable), and fruit (juice, puree, etc.) and/or some form of alcoholic beverage. It does not have dairy and likewise can be considered vegan, and safe for people with lactose intolerance. It does have its place as a dessert, but it can be used as a palate cleanser during meals in-between courses.
Sherbet/sherbert (I've heard it both ways) is similar to sorbet in terms of what it can be made from (ice/water, fruit, alcoholic beverages, etc.) but the difference is that it additionally contains some form of dairy, usually milk or cream. It is therefore not vegan (for the people who care), and might have enough lactose to affect people who have an intolerance to it (it's still much less dairy than something like standard ice cream).
tl;dr: Sorbet is like sherbet without the dairy, sherbet is like sorbet but with dairy.