Q.The seasonal variation means the variations occurring within :

Every observed value in a time series can be thought of as the joint outcome of four separate forces acting together: a secular trend (the slow, long-run direction), a seasonal variation (a pattern that repeats every year, tied to climate or custom), a cyclical variation (a longer, business-cycle-linked wave), and an irregular variation (one-off shocks with no pattern at all). Recognising which component is responsible for a particular movement in the data is the first and most important skill in time-series analysis, because trend-measurement methods (moving averages, …