Osteoporosis stands for “osteo” which is bone and “porosis” stands for pores in the bones.so when you get more holes in your bones, then it is called as osteoporosis. Osteoporosis means the density of the bones is less. So how do you measure the density of the bones? Density of the bones is measure e d by something called as the dexascanner- dual energy x-ray absorptiometry, that is the full form for a dexa scanner. Basically it is a long name for a machine which does a simple thing, it calculates the amount of calcium that is there in the bone, for a given centimetre square of the bone or for a given cube of a bone or a given volume of bone, we tell as how many calcium exists. So that gives us a measure of the strength of the bone. Is calcium the only thing that gives strength to the bone. No, collagen also gives strength to the bone. Collagen is like steel, it is stronger than steel, so if you have weak collagen then again you can have osteoporosis. Technically it is measured by the amount of calcium that is there in the bone.