Synthetic is usually used in the sense of synthesis, the combination of two or more parts, whether by design or by natural processes. It can also be used as in:

Synthesizer, a machine to create artificial sounds

Synthetic chemical or synthetic compound, produced by Chemical synthesis

Synthetic fiber, a fiber not made from natural (animal, plant) materials

Synthetic proposition, a concept in philosophy

Synthetic language, a language type using many complex word forms

Synthetic options position, a concept in finance