Simplify the following text for a Grade 6 native English-speaking person.
Original: The World Ocean , world ocean , or global ocean is the interconnected system of the Earth 's oceanic ( or marine ) waters , and comprises the bulk of the hydrosphere , covering almost 71 % of the Earth 's surface .
Simplified: The World Ocean , world ocean , or global ocean is a term used to define all the world 's oceans as one big ocean .