The spring 2018 version of Business Central was released on April 2nd. 2018.
The name was originally not supposed to have been announced officially until the keynote at Directions ASIA in Bangkok on March 15th. But MSDynamicsWorld.com had found out the name and leaked it in an article about it on March 12th. So Microsoft more or less where forced to changed announce it earlier.
Official announcement: https://cloudblogs.microsoft.com/dynamics365/2018/03/13/announcing-microsoft-dynamics-365-business-central-greater-impact-with-an-end-to-end-view/
The release was available in 14 countries.
Links: What's new in the Business Central Spring 2018 release