https://www.bleepingcomputer.com/news/microsoft/windows-10-may-2019-update-announced-insiders-get-it-first/

Microsoft has officially announced that the Windows 10 build 1903 feature update will be called the May 2019 Update. This update will be released to Windows Insiders first, who will test it for a month before it is made publicly available in May.

This update was originally thought to be named the April 2019 Update as build 1903 was listed under that name when using the Get-VMHostSupportedVersion PowerShell command.