Also referred to as a "data series." Series is a sequence of related data points that are plotted in a chart. For example, if you have a bar chart that shows the sum of kilobytes processed per hour by three web servers over the past six hours, each of the three web servers represents a series. Certain visualization types can support only a single series, while others can support multiple series.
When a series is plotted over a time range, it is referred to as a "time series." A time series displays statistical trends over time.
For more information
In the Search Manual:
In Dashboards and Visualizations: