Sync and async operations is about execution order a new task in relation to the current task. Two tasks on a table: current task and a new task
Synchronous(blocking) - implies that tasks will be executed one by one. A next task is started only after its previous task is finished. Task 2 is not started until Task 1 is finished
Asynchronous(non-blocking) – implies that task returns control immediately with a promise to execute a code and notify about result later(e.g. callback, feature). Task 2 is executed even if Task 1 is not finished
SO answer about sync and async: in iOS, in Android
[Paralel vs Concurrent]
