Fragrance Compound: What is it and is it safe to use/apply?

Hi - On the perfume-parlour.co.uk site you can purchase something marked "Fragrance Compound".

I contacted their support to ask what this is and got this reply: "We always advice to add carrier oil when using the fragrance compound."

Can anyone help me understand how Fragrance Compound differs from standard fragrance oil/spray and if there is any real risk in applying directly on skin?

Thanks!