The Jakarta EE name has been out for about a month, and even if Mike Milinkovich explained the names and concepts pretty well in his blog post And the Name Is..., there still is a bit confusion about how it all relates and I get questions around it whenever the topic comes up. I have tried to sum up some of it here. Hope it helps!
Java EE, or Java™ Platform, Enterprise Edition, is the name of the current platform governed by the Java Community Process (JCP). The latest version is Java EE 8, which was released in September 2017.
Jakarta EE is the name of the platform governed by the Jakarta EE Working Group. The first version will be Jakarta EE 8 which will be based on the Java EE 8 technologies transferred from Oracle to the Eclipse Foundation.
Eclipse Enterprise for Java (EE4J) is the top level project in the Eclipse Foundation for all the projects for creating the standards that will form the base for Jakarta EE. The EE4J Project Management Committee (PMC) is responsible for maintaining the overall vision for the top level project. It will set the standards and requirements for releases and help the projects communicate and cooperate.
Jakarta EE does not replace Java EE! It is the name for the platform evolving with Java EE 8 as a starting point. Java EE 8 will still exist, but there will not be any new versions of the platform.
Jakarta EE does not replace EE4J! It is the name of the platform based on the EE4J projects with Java EE 8 as a starting point.