What does synthetic mean?

Starts from a petrochemical (petroleum) source. Note some synthetic ingredients can come from "natural sources." The difference is that one is derived from sustainable resource (i.e. plants) and the other is not (i.e. petroleum).
Products have to perform, last, and not grow bacteria (another form of safety). At times this requires the use of synthetic ingredients—for example, the food-based preservatives we use. In addition, some ingredients occur in nature but aren't readily available in a commercial way.