You can find 5 main oceans in the world. If we includes the ancient oceans you can find 19 oceans on the planet.
What is Ocean
Ocean: The huge body of salt water which covers nearly three fourths of the earth’s surface.
Ocean: An ocean is a main body of saline water plus a principal element of the hydrosphere. Around 71% of the Earth’s surface (~3.6×108 km2 ) is covered by sea, a constant body of water that is customarily separated into several smaller oceans and primary oceans. Greater than half of this region is over 3,000 meters (9,800 ft) deep. Average oceanic salinity is about 35 parts per thousand (‰) (3.5%) and almost all seawater features a salinity in the range of 30 to 38 ‰. Scientists estimate that 230,000 marine species are presently known, however the total could be approximately 10 times that number.
There are five major oceans of the world,
Covering around 155 million square kilometers (59 million square miles) and containing greater than half of the free water on planet, the Pacific is by far the biggest of the world’s ocean. All of the planet's continents could fit into the Pacific Ocean.
The Pacific Ocean is the largest ocean in the world, covering greater than one-third of the Planet's surface and almost half of World's water surface. The world's 2nd largest ocean is the Atlantic Ocean, which addresses one-fifth of the whole surface area of our planet. The third biggest ocean on earth, the Indian Ocean, is encircled by the Southeast Asia in the north and Arabian Peninsula, Australia in the east and Africa in west. The Southern Ocean has been described relatively recently, in 2000 and contains the waters around Antarctica. Positioned around the Arctic Circle, the Arctic Ocean is the littlest and the shallowest ocean on earth. South China Sea, one of the biggest seas after the 5 biggest oceans of the world, encompasses hundreds and hundreds of islands.
The Marianas Trench (or Mariana Trench) is actually the deepest part of the world's oceans and the deepest area on the surface of the planet's crust. It has a maximum depth of approximately 11,033 meters (36,201 feet) and is positioned in the western North Pacific Ocean, towards the east and south of the Mariana Islands, close to Guam.
The trench forms the boundary among two tectonic plates, in which the Pacific Plate is subducted under the small Mariana Plate. The base of the trench is farther below sea level compared to Mount Everest is above it (8,850m/29,035ft). At the base, the water column above exerts a pressure of 108.6 MPa, over 1000 times the standard atmospheric strain at sea level.