It translates to "The Flak Tower".
"Das Flakturm" is featured as a soundtrack of the computer game Medal of Honor: Airborne (the 11th installment of the Medal of Honor series), composed by Michael Giacchino.
In the game, the sixth and final mission takes place in a partially destroyed tower called "Der Flakturm" - a huge, concrete structure, with several 128mm FlaK 40 anti-aircraft guns at the very top.
Flak is actually the shortened version of Flieger or Flugabwehrkanone, which means "cannon for defense against aviation." While turm means tower.