When first introduced in 1606, the Union Jack was simply known as the British flag or flag of Britain. The name Union first appears in 1916-25 but what of the term Jack? Various theories exist, but the bulk of evidence indicates use of the word in its diminutive sense. Before 1600, Jack was certainly used to describe a small flag flown from the mast mounted at the end of the bow sprit. And by 1674, this flag was described formally as his Majesty's Jack and officially acknowledged as the Union Jack.