A sweep can be compared to the windshield wipers in your car. They start from one position and move to the other. Both points can be referred to as starting and ending frequencies, depending on the direction of the sweep.
There is one more variable here which determines how slow or fast such a sweep goes as it moves in incremental (or decremental) steps. Theses steps are increments by which a sweep progresses. If this value is 1Hz, then the sweep will proceed in 1Hz steps, eg. 292—293-294, and so on.