If it is an exercise that uses dumbbells (i.e., tricep kickbacks or dumbbell bicep curls--not barbell bicep curls), then it is referring to the weight of each dumbbell. So if it says the target weight for a dumbbell exercise is 16 lbs., you would use a 15 lb. dumbbell and a 1 lb. glove or wrist weight.
If it is an exercise that uses a barbell, it would be the total weight your barbell should weigh including the weight of the barbell. If you are using dumbbells for a barbell exercise, you would need to half the target weight to find what each dumbbell should way. For example, a barbell shoulder press with a target weight of 30 lbs. can be done with two 15 lb. dumbbells.
Hope that helps!