Coordinated Universal Time abbreviated to UTC, is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time at 0° longitude; it does not observe daylight saving time. For most purposes, UTC is considered interchangeable with Greenwich Mean Time (GMT), but GMT is no longer precisely defined by the scientific community. 

The first Coordinated Universal Time was informally adopted on 1 January 1960, but the official abbreviation of UTC and the official English name of Coordinated Universal Time (along with the French equivalent), was not adopted until 1967. 

The system was adjusted several times, including a brief period where time coordination radio signals broadcast both UTC and "Stepped Atomic Time (SAT)" until a new UTC was adopted in 1970 and implemented in 1972. This change also adopted leap seconds to simplify future adjustments. This CCIR Recommendation 460 "stated that (a) carrier frequencies and time intervals should be maintained constant and should correspond to the definition of the SI second; (b) step adjustments, when necessary, should be exactly 1 s to maintain approximate agreement with Universal Time (UT); and (c) standard signals should contain information on the difference between UTC and UT."
When was UTC adopted?
When was the official abbreviation adopted?
What does it stand for?
What is it?
Who uses it?
How close to is it to mean solar time?
IS it interchangeable with anything?
What?
Is GMT still defined?
Does UTC recognize daylight savings time?
Have their ever been any adjustments?
What was it once coordinated with?
Until what happened?
When?
When was its implementation?
What did it also adopt?
For what reason?
It is stated that carrier frequencies should be what?
What should be exactly 1 s?
Why?
1 January 1960
 1 January 1960
1967
1967
Coordinated Universal Time
Coordinated Universal Time
the primary time standard
the primary time standard
the world
the world
1 second
1 second
yes
 with Greenwich Mean Time
Greenwich Mean Time
Greenwich Mean Time
no
no longer precisely defined by the scientific community. 
no
 it does not observe daylight saving time
yes
The system was adjusted several times
both UTC and "Stepped Atomic Time
both UTC and "Stepped Atomic Time
a new UTC was adopted
a new UTC was adopted
1970
1970
1972
1972
leap seconds
 leap seconds
simplify future adjustments.
 simplify future adjustments.
maintained constant and should correspond to the definition of the SI second
maintained constant and should correspond to the definition of the SI second
step adjustments,
step adjustments,
to maintain approximate agreement with Universal Time
to maintain approximate agreement with Universal Time