What process describes the decrease in bone density?

The process that describes the decrease in bone density is osteoporosis. Osteoporosis is a condition characterized by the reduction in bone mass and the deterioration of bone tissue, which leads to an increased risk of fractures. This condition often occurs due to an imbalance between bone resorption and bone formation, where the body either loses too much bone or makes too little bone.

Osteogenesis refers to the process of bone formation, while osteomalacia involves the softening of bones due to a deficiency of vitamin D, leading to improper mineralization rather than a decrease in density per se. Osteoarthritis is a degenerative joint disease that affects cartilage and is not directly related to bone density. Thus, osteoporosis is specifically recognized for its impact on reducing bone density, making it the correct answer.