At least in java.time (which I believe an inspiration for Temporal) Duration (https://docs.oracle.com/en/java/javase/21/docs/api/java.base...) is a time-based measure of time. For example, 5 hours, 59 minutes, and 15 seconds.

Period (https://docs.oracle.com/en/java/javase/21/docs/api/java.base...) is a date-based measure of time. 2 years, 3 months, and 4 days.

Interval (https://www.threeten.org/threeten-extra/apidocs/org.threeten...) isn't built into java.time, however, it is in the popular threeten-extra library. The docs say "An interval represents the time on the time-line between two Instants." The main difference being that Interval is anchored to the timeline while Duration and Period are not.