Brain attack. 2 kinds of stroke: ischemic or hemorrhagic. Ischemic (either thrombotic or embolic) is like a clogged drain in your house. Hemorrhagic is like a burst pipe. In either case, you don't get water flowing where you need it. Same w/stroke - you lose blood flow to vital areas in your brain (are there non-vital areas?). Without blood flow, brain dies. So if you think you're having a stroke, call 911.
Brain function loss. I assume you mean cerebral stroke (brain). There are heat strokes, etc. Brain stroke refers to a rapid loss of brain function. This can be due to loss of blood supply to the brain tissue or a brain bleed (hemorrhage). A transient loss of blood supply whereby the brain function is immediately restored when the blood supply is restored is called a mini stroke, ie, "transient ischemic attack".