Invisibility Work Or Spells is a category of spells found in most traditions of magic. In the practice of hoodoo/rootwork, such usually takes the form of the infamous black cat bone which is believed to make one invisible. Since the harming of cats is a huge no-no, one can substitute black cat hair for a black cat bone in invisibility spells.
Invisibility work or spells are believed to work by making people over-look the practitioner. One is not actually invisible. To help explain it further, have you ever misplaced an item such as keys and have torn-up your home looking for them only to discover they were laying right under your nose and in plain view the entire time? This is how invisibility spells are believed to work.
Invisibility work is good for many situations. One use of such is when gathering graveyard dirt. The practitioner can gather graveyard dirt in broad daylight and even with other people being in the cemetery, all without fear of being accosted by bystanders. Some people use invisibility work on the Police and other authorities to either not fall prey to such things as racial profiling, to avoid harassment, or to even hide their criminal activities. The one area I was taught not to use invisibility work on is one's vehicle. The shop owner who taught me this claimed she had a few customers over the years who told her their sad tales of putting an invisibility spell on their vehicle only to experience being rear-ended by other drivers who "didn't see them".