What is meant by "projection" "volume" and definition related to BBL surgery?

Good question.
Volume is the amount of fat we place during a BBL. The number of cubic centimeters (cc). There are 354 cc in a regular can of Coke. 1 cc equals 1 ml (milliliter). Some patients have larger buttocks and naturally need more volume, others want more volume and some patients desire a more natural look and a more modest change and will require a smaller volume.
Projection is the distance that the buttocks will extend out from the rest of the frame of the body. For example, if you undergo a breast augmentation you will place an implant and it will increase the volume of the breast (make it bigger), but it will also increase the projection (the distance of your breast projecting or coming out from your chest.
Definition relates to the tissues around your gluteus. For example, if you have a lot of fat in your love handles, inner thighs, outer thighs, lower back then removing fat from all of these areas will get a better transition between these areas and your gluteus and give you more definition of the buttocks.