This event is more a commemorative event than a holiday (The word "holiday" does not describe this event), being the only one of this class.
14th Nissan it is a commemorative event held mainly among Jehovah's Witnesses, which is the commemoration of the death of Jesus Christ. Which is celebrated on the 14th of the month of Nissan of the Hebrew calendar, corresponding to the months of March and April without specific day of the Gregorian calendar. It's a totally different day traditional Easter today commemoration, as many before it for days off events is replaced, and the commemoration is done either in a Kingdom Hall or an event hall , and it is organized during sunset (if be possible due to certain circumstances). The meeting is open to the public and talk about issues related to the death of Jesus Christ (prophecies, life of Jesus Christ, etc.), the representation of the bread and wine with Jesus Christ, the anointed ones, etc.