VBA is simply an object library containing objects, methods, and properties that allow for programming within office as well as other microsoft products i.e. reflections.
VB is nearly identical to VBA as far as code syntax is concerned. In VB, however, the objects, methods, and properties have more capabilities than VBA. VB is also usually used to refer to the IDE (Integrated development Environment). This is the independant program that you design interfaces and write code within. In VBA the development environment is just an extension of whatever program you are i.e. Access, Excel, Word, Reflections.... Also the VBA development environment in different programs can be different.
There are many other more complicated capabilities within VB that are not possible in VBA like EXE compiling, COM programming etc....