Really not a lot, although often it means the same thing to many people the real difference is that pruning is generally on a much smaller scale with maintenance like pruning leaves and dead branches or diseased parts being what is achieved. Trimming often means shaping a tree by cutting healthy parts in order to maintain its shape which is a bit more involved. Both will be necessary but can often be done at the same time so it’s not something you need to worry about as we will take care of whatever is necessary and best for the tree