It has two connotations.
Great Britain as a geographic entity refers solely to the single island that houses most of the nation as we know it.
Great Britain as a political entity is the name given to the majority of the UK, excluding Northern Ireland. This includes much of the outlying islands...
I don't think that's strictly true. The land mass on which we're currently stood would still be known as Great Britian, regardless of the political status of the countries that occupy it.
Much like the island of Hispaniola would remain Hispaniola even if Haiti and the Dominican Republic...