It's a name that was given in the Middle Ages to a Jewish rabbi miracle worker who could bring about cures and healing, as well having mystical powers to foresee or interpret events and personalities. They were considered to have a "direct line" to Heaven evoking God's mercies and compassion on suffering human beings.
Not many people with this title have been recorded, and none have it today.
The most famous one was the founder of Hasidism, Rabbi Israel ben Eliezer, who is known as "THE" Baal Shem Tov. Few people are aware that there were some other rabbis who bore this appellation.