A "decker bus" refers to a type of bus that has two levels or floors. It is taller than a regular bus and allows more passengers to be seated. Full definition
I took a double decker bus tour and I also visited Uxmal and Celestun. (bigtravelnut.com)
You definitely want to allow a half to full day to enjoy the zoo and check out all the fascinating exhibits and even take a double - decker bus tour as your first introduction to the park. (travelphotodiscovery.com)
Everton will come out true to their manager's style, parking a double decker bus in front of their own net and looking for any attempt to counter. (anfieldindex.com)