Starter and levain are essentially the same thing. I tend to refer to starter as the small amount of dough I am regularly feeding and maintaining over time. When I’m ready to mix up a dough, I will first build up a larger amount of my starter, which I call my levain—the starter I am adding directly to my dough. Most often I use the same flour to feed my starter as I do to build my levain. But if I wanted to mix up a 100% whole wheat recipe, I would want to take a small bit of my starter and begin feeding it 100% whole wheat flour for a day or two to get my starter microbes adjusted to the new flour feed mix.