A time-series is a

In retail or manufacturing, time-series are important because they are the most

The graph here above represents, as two

There are two main

- The
**period**which represents the aggregation level. The most common periods are month, week and day in supply chain (for inventory optimization). Call centers typically rely on quarter-hour period (for staffing optimization). - The
**horizon**which represents the the number of periods ahead that need to be forecasted. In supply chain, the horizon is typically equal or greater to the lead time.

Then, there are further subtleties related to the definition of the period itself, mostly because of calendar artifacts. For example, one can decide that the monthly aggregation starts on the Nth day of the month (instead of the 1st), but if N is greater than 28, it causes problems because not all months have more 28 days.