Lilac Point is a term used to describe a cat's coloring. It means that the cat's body is one color (usually white, cream, or fawn) but has pinkish-grey points (face, paws, and tail). The points are a delicate grey; the pink isn't more than a light tinge.
The color described as lilac on the points is the same as a lavender colored cat. Why they use one word for the entire cat and another for the just the points is a mystery.
Lilac pointing in cats is caused by an odd allele of the gene that activates hair pigmentation. In these cats it is only activated at low temperatures. This means that hair follicles on the trunk of the cat, receiving full body temperature, do not express the gene, but those on the extremities are cool enough to become colored. If you were to bandage a foot or ear, the higher temperature would cause it to lighten in color over time. Likewise, cold weather and illness can also cause changes in body temperature and fur color.
There are also other colors of point, such as seal point, chocolate point, blue point, and smoke point.