Union Jack 5' x 3'with eyelets for flying from a pole or mast.
And yes, it is a Union Jack. Although the flag has it's origins at sea, being flown from all types of English and Scottish vessel from 1606 and known unofficially in Admiralty circles as the "Union Jack". Shortly thereafter its use was restricted to vessels under the pay of the King presumably to avoid confussion.
Parliament finally gave official approval for the name "Union Jack" in 1908 (three hundred years late!) and stated that "the Union Jack should be regarded as the national flag".