Seasonal component is short-term in nature and its effect is seen according to the seasons. The significant variations occured in the variable quantity of time series at fixed period of time in the year say winter, summer, monsoon. For example, a spurt in demand for woolen clothes in the winter, a spurt in the sale of ice-cream and cold drinks in the summer, increase in demand for umbrellas and raincoats in the monsoon, increase in the sale of readymade garments and footwears during the religions festivals, etc. are the illustration of seasonal fluctuation.

From the study of seasonal component traders and manufacturers of seasonal goods plan for periodical stocks to take care of the demand of such goods. Generally, the duration of oscillation of seasonal fluctuations is of one year. The seasonal component is denoted by the symbol S_t.

Generally the period of oscillation of seasonal component is less than a year. To study the seasonal component it is necessary to have the value of series in short-term. If the yearly values of the variable are available then it is not possible to obtain the information of seasonal component.