The encanto, also known as "the fascination", is the unique ability of vampires to almost hypnotically convince other humans, both mundanes and Shadowhunters, of almost anything and to persuade them into doing almost thing they're told.
Performing the encanto is a skill practiced by vampires and developed over time, so it is typically older and more powerful vampires who often use it. Meanwhile, Shadowhunters undergo training to resist it.
In the 1700s, Paris, though avoided by most other Downworlders, became a sort of terrain of vampires, because of their ways, and a huge part was the encanto which enchanted many of the country's nobles.
When Raphael Santiago was first Turned in 1953, he was quick to learn and perfect his encanto. Magnus Bane wondered if it was because Raphael had been practicing, or if it came naturally to him because of his innate ability to impose his will on others.