Who are the ‘Synagogue of Satan’?

What or Who are the ‘Synagogue of Satan’?

Many people ask who or what are the “synogogue of satan” mentioned in the Book of Revelation, as they get a wrong impression of Jews from a statement made in the Book of Revelation chapter 2 verse 9 where it mentions a certain phrase that was understood 2000 years ago in the first Century persecution that is no longer understood today by readers without the cultural context of 2000 years ago and thus it causes  many misunderstandings!