Definition - What does Parasite mean?
A parasite is a type of biological organism that lives on or inside another organism referred to as the host and lives off it's host. A parasite receives its nutrients from the host. The term can also be applied to human behaviour where a person receives advantages or support from another without providing any good in return. The common defining characteristic for both uses of the term is this type of one one-sided relationship.
Safeopedia explains Parasite
Parasitism is a form of symbiosis where one organism takes nutrients or support from another and returns nothing, or causes only harm to the organism providing support. Parasitic lifeforms in biology can have a large impact on host organisms and can change an ecology. Some have the ability to change their host's phenotype and their role within a food web significantly. Some say they may have a functional role in regulating species within an ecology.