Fragrance oils (also called perfume oils) are usually synthetic; chemists analyse the plants’ components and reproduce their chemical compositions. There are literally thousands of various compounds that each have their own scent…that blended together create a fragrance oil.
Fragrance oils are essentially a "pleasant" aroma, and many modern perfumes are created using fragrance oils. It is possible to create almost any aroma in a fragrance oil, unlike an essential oil, which is extracted from an appropriate plant.