What is a Preset?
A preset is essentially "information".
Each preset is a list of parameter's that controls how the synth is setup.
A synth is made up of amps, filters, effects, and other controls.
A preset simply stores these setting so they can be easily recovered.
Back in the old days, there were no presets.
A sound was created by connecting cables between the amps, filters, etc.
Now presets are used to do the same thing and are considerably easier to use.
Presets are the key to how a synth will sound.