It's true that it's a bit of an expansion of the word "business", but it doesn't really mean "something to do with commerce". It's just the parts of the code that handles the rules of the system that directly enable the user's goals, and not any of the auxiliary, supporting infrastructure. So for a DAW business logic is pretty broad, true, but it would be stuff like, faders or muting a track and the effect on the mix, whether you can copy-paste a snippet of audio, and routing audio through plugins. And not things like the file format of a project, or the code that interprets hardware interfaces.