The ocean is the vast body of salt water that covers over 70% of the earth’s surface. There are also subdivisions of this body, which can be referred to as separate entities using the word “ocean” as with the Pacific Ocean, Atlantic Ocean, Indian Ocean, etc.
Contaminant refers to all the bad things in drinking water, including man-made chemicals. The term organic contaminant specifically refers to naturally occurring contaminants, such as debris or even Manganese, that are bad for human health.
An organism is any individual entity that exhibits the properties of life. You’re an organism, your dog is an organism, and those creepy little single-cell prokaryotes are organisms.
For the sake of keeping this glossary under a thousand pages, here is a simple definition. Osmosis is the tendency of a fluid, usually water, to pass through a semi-permeable membrane into a solution where the concentration is higher. Water tends to dilute (water down) the concentrated side until the fluid on both sides is equally concentrated.