The phrase "main deck" refers to the primary or most important level of a ship or aircraft where most of the activities and operations take place. Full definition
The beautiful master suite that spans the full width of the vessel (and occupies the entire bow on main deck) offers all the comforts of home. (scubatravel.com)
All guests have access to our Great Room with its wall of windows, main deck with hot tub and our private beach with helicopter pad. (awesomeview.com)
The nearby showers and toilets are shared with other Main deck cabins. (acrossnz.com)