Necessary and Sufficient - a feasiblity test in real-time theory which will pass all service sets that can be scheduled and will never fail a set that can be scheduled (more precise than a sufficient test which may falsely reject some service sets, but will never falsely ok a service set than can not be safely scheduled).
Nesting - when a construct is used inside the same sort of construct - one inside the other - e.g. if a critical section encloses another critical section the critical sections are said to be nested.
Non-Blocking - when a request for a resource can not be met immediately, the RTOS can either block the calling thread until it is available or return it an error code indicating why the request can not be met and letting the thread go on - the latter is non-blocking.
Nor Flash a flash memory device which is normally erased to all 0ís and writes are bitwise masked in with an or operation.