A DatetimeIndex is used to represent a set of dates and times. These are extensively used in time series data where samples are taken at specific intervals of time. To briefly demonstrate this, the following code creates a range of 5-hourly time periods and uses them as the index for this series.
The type of the index can be seen to be a DatetimeIndex.
The underlying representation of the date/time is a 64-bit integer, making lookups by date and time very efficient.