Tengelmann is a nationwide chain of German supermarkets.
It is considered one of the slightly better brands of supermarket. I.e. more upmarket than Penny-Markt or Lidl. But not as upmarket as MiniMAL.
The supermarket is actually officially called: Kaiser's Tengelmann AG
The Tengelmann company is actually a group of subsidiaries which include OBI and Plus as well as a small handful of others.
See also: Supermarkets