Time-Series Analysis #Statistics permanent It can be divided in to 4 parts:
- Long-term trend
- Cyclical variation
- Seasonal variation
- Random variation
Trend
A Trend is a long-term, relatively smooth pattern or direction exhibited by a series, with a duration of more than 1 year. 
It can be linear but can also be like this: 
The difference between Cyclical variation and Seasonal variation can be divided into time and factors. Cyclical is usually more than 1 year, since Seasonal is always within 1 year. And Seasonal is more because of the season, festival, and weather.
Random variation is due to the unpredictable reasons. But it actually appears in almost all time series, so one of the objectives is to find a way to reduce such random variation to make accurate predictions of the time series.