An organism is another term of a living thing. It can be an animal, it can be a plant, or it can even be a single-celled form that has a life. Take note that this is the description of an organism as stated in biology but there are also instances when an organism can be used to mean other things.
For example, in a structure, an organism may be used to describe the parts of the structure that is still likened to those who are alive. People may say that children are the hope of the current social organism.
The word organism will stand for the structure as a whole. It can also refer to a structure that can provide a life form such as one of the organs of the body.