My understanding is B4X is combination of both
@Sagenut and
@Sandman answers.
B4X is a collection of the tools in this case the IDE to create cross platform apps using the programming language which is also call B4X.
B4X IDEs consists of B4A, B4J, B4i and B4R.
So I can say the term B4X can be used interchangeable between the software and the programming language.
A B4X programmer/developer is someone who can write in B4X programming language using B4X tools.