triple-decker

Short definition from Wiktionary

Noun

1. 1
   Something with three levels or storeys: A bus with three storeys.
2. 2
   Something with three levels or storeys: A three-storey apartment building.
3. 3
   Something with three levels or storeys: A sandwich consisting of three levels of filling between four pieces of bread.
4. 4
   Something with three levels or storeys: A headline that is three lines long.