Lvl 80 boosts and shared slots
One for each expansion would be two. One for Heart of Thorns, and one for Path of Fire. Unless one has purchased extra Shared Inventory Slots, one would have only two after having purchased both expansions.
No free Shared Inventory Slot was given when they were first introduced in January of 2016. The Spring 2016 Quarterly Update on April 19, 2016 added a free slot to accounts with Heart of Thorns unlocked, and raised the limit of purchasable slots to 10.