A parasite is an organism that lives in another organism, called the host, and often harms it. It is dependent on its host for survival – it has to be in the host to live, grow and multiply. A parasite cannot live independently.
Although a parasite rarely kills the host, in some cases it can happen. To a certain extent, if a parasite does kill its host it has failed as this means it will need to find a new home. The parasite benefits at the expense of the host – the parasite uses the host to gain strength, and the host loses some strength as a result.
The word “parasite” comes from the Greek “parasitos”, with para meaning “alongside”, and sitos meaning “food” – therefore meaning “eating at the side of, as one would when seated at the same table”.
It was in the 18th century that the word parasite entered the English language as a biologic term; before that it referred to humans, such as a relative or friend who lived at the expense of another person.