Organs
The body's organs are usually vital to the body's existance, hence vital organs.
An organ can be defined as "a differentiated structure", "consisting of cells and tissues, performing some specific function in an organism."
So any group of specialised tissues fulfilling a specific function is an organ. However not all organs are vital !
Each organ is not a separate entity, for instance the heart and lungs are very closely related and work in unison as do all of the body's organs. This is why we are refered to as organisms i.e. a collection of organs, all working together.
Examples of vital organs are:
Examples of non-vital organs are:
References
www.britannica.com