“a simplified description, esp. a mathematical one, of a system or process, to assist calculations and predictions”
“a representation of something big”
a map
the circular flow diagram (economic)
diagrams of the human body (biology)

“producing a computer model of something”
“a simplication of reality”
Simulation is used in
modeling of natural systems or human systems in order to gain insight into their functioning.
simulation of technology for performance optimization, safety engineering, testing, training and education.
Education, usage of computer 3-D modeling in order to explain how two chemicals bond to each other and what angles they form
War scenarios, for example, scientists test how a bomb will affect the city and the people living in it.