daylight saving time; summer time
Refers to the system of advancing clocks during part of the year to make better use of daylight. サマータイム is also common in everyday discussion.
Japan currently does not observe daylight saving time.
In Europe, many countries switch to summer time in spring.
That country introduced daylight saving time a few years ago.
Many countries switch to daylight saving time in March.
Daylight saving time ends in October.