That's not accurate and there is a difference in meaning between an ocean and a sea. An analogy to land would make oceans continents and seas countries. Seas are smaller bodies of water.
Most people are taught that there are 4 oceans but this model has recently been extended to a 5 ocean model. Within the oceans are seas, and as an example the Indian Ocean contains the Andaman Sea, Arabian Sea, Bay of Bengal, Gulf of Aden, Mozambique Channel, Persian Gulf, Red Sea and the Timor Sea.