The first thing to look at is the part of the lump on the waist, is how the hard lump relates to the activity and the skin. If it is under the skin and relatively free, you can go and feel the activity yourself, proving that it is some swelling under the skin, mostly lipoma or fibroma, which are benign swellings, this kind of lump does not need to be bothered with it, it is a benign tumor under the skin. If the hard bumps remain unchanged with activity, especially around the bones, consider that it may be ossification or sclerosis of the interspinous ligament or the generation of bone, and do not exclude the possibility of a deep tumor. Therefore, it is difficult to answer the specific cause of a hard bump simply on the waist, but it is recommended that you can go to the hospital to get an ultrasound, under the guidance of which you can see exactly what the nature of the bump is, whether it is hollow, solid or substantial, whether there is ossification or calcification, or even a CT to see the condition of the tissue surrounding its depth, which may be of some more help.