As an example, the solutions of ordinary differential equations can be represented as a time series, similarly, how stock prices evolve as function of time is another example of a typical time series, or voice records and many other examples.
Not all sequential data may however have a time stamp, texts being a typical example thereof, or DNA sequences.
The main focus here is on data that can be structured either as time series or as ordered series of data. We will not focus on for example natural language processing or similar data sets.