What The Term Schematic Is Used To Refer To In General?

The term schematic is generally used to refer to graphical representations of structure or components of any system. These graphical pictures give us an abstract view of that system. These are not actually realistic pictures.

The schematics are usually drawn to explain something more clearly. These schematics may or may not depict the complete system that is they give graphical/symbolic representation of only those parts that they want to describe and ignore the irrelevant details of that system.  And some times the schematics may add some extra components that don't exist really just for explanation.

In these graphical pictures, different types of symbols are used to denote real element/components of the system. By using these symbols schematics show that how these components of the system are interconnected together, how they work and how they affect each other's performance while the system performs its tasks and all the stuff like that.

These schematics are used in variety of domains where we need to describe the working of our system /machine to the workers in a simple way.
The schematics are also  widely used in education field where these diagrams help the students to learn and understand some structures, devices, scientific theories etc.