"A symbol of courage given to those who have overcome the challenges of a shrine."
Spirit Orbs are given to Link upon successful completion of a Shrine from a Sheikah Monk. After four orbs are collected, they can be exchanged for either a Heart Container or a Stamina Vessel by praying at a Goddess Statue.
As there are 120 Shrines located in Hyrule in the base game, there are also 120 Spirit Orbs. Sixteen additional Shrines were added with the introduction of The Champions' Ballad DLC pack, four of which giving Spirit Orbs, raising the total to 124.