Great Britain is the name of the island.
The kingdoms of England and Scotland, the Principality of Wales and the six counties of Northern Ireland are united in a single sovereign state - the United Kingdom of Great Britain and Northern Ireland. Northern Ireland is part of this state but not part of Great Britain.
Great Britain is the island, the largest island of the UK, on
which is found the majority of the territory of England, Scotland
and Wales. The Kingdom of Great Britain ceased to be a nation state
in 1801 when the United Kingdom of Great Britain and Ireland was
formed. The modern-day name of the United Kingdom of Great Britain
and Northern Ireland was formally adopted in 1927. It is incorrect
to refer to the country of the UK as Great Britain or, as is often
heard, England. These terms are not interchangeable.
The term Great Britain is rarely used in the UK; its use is relegated to some sports under which the nation, for some reason, competes. The international standards GB and GBP have also been imposed on the UK but they are incorrect.