Union Flag or Union Jack: Which is correct?

In which situations should the terms 'Union Jack' and 'Union Flag' be used?

Flag of the United Kingdom History, Meaning, Colors & Design

Curious Questions: How can you tell if the Union Jack is upside

Search Forces Network

Curious Questions: How can you tell if the Union Jack is upside

Is it the Union Flag or the Union Jack and what is the correct way

Flags of Empire: National Ensigns of British North America and the

UK flag protocol

The Story Of The Union Jack: The National Flag Of The United

Diagram Showing Correct Way Fly Union Stock Vector (Royalty Free

Search Forces Network