There is not way to tell from palpation exactly what type of lump this is. This lump needs to be examined by a veterinarian. They will do a fine needle aspirate (a small needle is inserted into the lump to collect cells for examination under the microscope) to identify the lump. It may be a cyst, abscess, lipoma (fatty tumor), or a cancerous growth.
My Cat Has A Lump Above Her Front Left Leg Which Moves It Around When You Touch It. It Does Not Seem To Cause Her Any Pain When You Touch Or Move The Lump Do You Know What This Is?
Unfortunately, it's not a good idea to just "guess" about this situation. It could be anything from a simple cyst to a cancerous tumor, and if your cat is an outdoors cats, it could be an abscess that has somewhat healed. Take her to the vet. One thing I do know: If you can move it around; it's not connected to surrounding tissue, it's probably a cyst.
After my cat got her rabies vaccine a large lump was left on her leg. If it starts to grow/devolep more than I suggest you take her to the vet, my cats bump started to reduce in size within a month and after about two it wa gone