The Battle of the Bulge was a last-ditch effort by Germany to turn the tide of WWII that had distinctly gone against them. With massed forces, they attacked the enemy, creating a large bow in the lines, aka - a bulge. Battlefront is focusing on the Battle of the Bulge with their next book, Bulge: American - Forces on the Western Front, 1944-45, coming next month for Flames of War.
From the announcement:
Winter is coming! Bulge: American takes us to the German Ardennes offensive during the winter of 1944 and onwards, and brings a range of new equipment to the frontline!