jorgecarleitao commented on pull request #11138:
URL: https://github.com/apache/arrow/pull/11138#issuecomment-917581003


   You are right 👍 
   
   I understood that comment to differentiate it from `Duration`, that denotes 
a physical time interval. Specifically, my understanding is that 
`Duration[s](1)` equals 1 second as per its definition of [atomic clocks and 
stuff](https://en.wikipedia.org/wiki/Second).
   
   In opposition to an `Interval`, that corresponds time units that are 
constructs associated with a calendar (historically associated with the Earth 
and moon movements), such as "Month", "day", etc.
   
   The main difference (in my understanding) is that 
`add_duration(now,duration(MS_IN_DAY)) - now = duration(MS_IN_DAY)` and 
`add_interval(now,interval(1d)) - now = interval(1d)`, but `duration(MS_IN_DAY) 
!= interval(1d)` because we may cross a (calendar) offset, either due to a leap 
second, leap hour (daylight, which I forgot about in the comment above), leap 
day (February), etc.


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