The term "decker" usually means stacked one on top of another. They call two trailers connected a "double bottom", so perhaps three connected trailers would be a "triple bottom".
A three-story apartment building is often called a triple-decker; a sandwich with three pieces of bread is often called a triple-decker.
it's called a double Decker bus
The sword is called the Nocturne.
it is called The Deuce
The Germans in World War 1 called it the Tri-decker. Triplane or Tripe
Elmer Decker's birth name is Elmer Ellsworth Decker.
Holly Decker's birth name is Holly Jean Decker.
Julia Decker's birth name is Julia Anne Decker.
Max Decker's birth name is Maximillian Alexander Decker.
Spence Decker's birth name is Spence Sherrel Decker.
Unusual. It's commonly referred to as an "upper-decker."
It's just called a bus or a coach, unless you are thinking about the ones with an upstairs which is known as a double-decker.