What degenerative disc disease actually is
The discs between your vertebrae are mostly water. They work as spacers and shock absorbers, and they let your spine bend without grinding bone on bone. With age they lose water content, flatten, and stop cushioning as well as they did.
That is degeneration, and to a degree it happens to everyone. It becomes degenerative disc disease when the flattened disc starts producing symptoms: back or neck pain that comes in waves, stiffness first thing in the morning, pain that worsens when you sit or bend and eases when you walk, and sometimes numbness, tingling or weakness running into an arm or leg.
Once a disc has lost height, the load it used to carry shifts onto the facet joints behind it. That is why so many imaging reports read "degenerative disc and facet disease" together, and why the pain often spreads beyond the original level.
Inflammation is what turns a worn disc into a painful one. It is also the part that treatment can realistically influence.