What is Ramsay Hunt syndrome that Justin Bieber has been diagnosed with?News India (All States)

The popstar took to Instagram to share a video showing inability to move his face muscles due to Ramsay Hunt syndrome

source https://www.livemint.com/news/world/what-is-ramsay-hunt-syndrome-that-justin-bieber-has-been-diagnosed-with-11654915720294.html