ISTQB does not distinct between these (it reads "Branch/decision coverage") but some sources do say it is different. I would have two question. The essential one is about the difference. And the other one - does this whole concept belongs under the unit testing? Or white box testing? Thanks
From the ISTQB:
branch coverage is closely related to decision coverage and at 100% coverage they give exactly the same results. Decision coverage measures the coverage of conditional branches; branch coverage measures the coverage of both conditional and unconditional branches. The Syllabus uses decision coverage, as it is the source of the branches. Some coverage measurement tools may talk about branch coverage when they actually mean decision coverage. (c) ISTQB foundation book.