Learn in the textbookClassifying Data by Attribute and Structure
DefinitionTime-series data (時系列データ) records the same subject again and again as time passes.
ExplanationDaily temperatures, monthly sales, and yearly population counts are examples. Lined up in time order, they reveal trends up or down and seasonal swings, and line charts are the usual way to show how they change.
AnalogyLike height marks carved on a doorframe. The same child is measured each year, so you can see how they grew.
Memory hook"Series" means things lined up one after another, so a time series is simply values lined up in time order.