Greenwich Mean Time (GMT) is often confused with Coordinated Universal Time (UTC). GMT and UTC share the same current time in practice, but there is a basic difference between the two. GMT is a time zone and UTC is a time standard.
GMT is a time zone officially used in some European, African, and other countries. The time can be displayed using both the 24-hour format (0 - 24) or the 12-hour format (1 - 12 am/pm).
UTC is not a time zone, but a time standard that is the basis for civil time and time zones worldwide. This means that no country or territory officially uses UTC as a local time.
Neither UTC nor GMT ever change for Daylight Saving Time. However, some of the countries that use GMT switch to different time zones during their Daylight Saving Time periods. For example, the United Kingdom is not on GMT all year, it uses British Summer Time (BST), which is one hour ahead of GMT, during the summer months. Seems to me all Daylight Saving Time should adopt the British acronym and call it for what it is - BST, for Bull S... Time.