One is set, the other is estimated
A target
A target, or quota, is a commitment for a period. It is decided in advance from business need, capacity and ambition. It does not change when the month goes badly, and that permanence is the point: it is the standard against which performance is judged.
A forecast
A forecast is an estimate of what will actually close, built from the deals in your pipeline and updated as they move. It should change whenever reality changes. A forecast that never moves is not a forecast, it is a target being repeated.
