What is the easiest way to describe gingivitis/periodontal disease to a person?

Inflamed Gums: Bacterial film builds up under the gums creating inflammation and eventual underlying destruction.

Gum inflammation: Gingivitis is inflammation of the gums. Reversible & not associated with bone loss. Periodontitis is a chronic, incurable but treatable disease where supporting bone around teeth is lost. There are predisposing risk factors such as; smoking, stress, genetics, medications, systemic diseases, poor home care.

Internet: Internet, google for the picture (image) of periodontitis vs. Gingivitis, a wiki description of both, and the picture of the periapical xray of perio vs. Gingivitis. The best is having a joint consultation with a dentist/periodontist.

Plaque buildup: Bacteria, when not removed regularly, irritates the margin of the gums and you may experience bleeding when you brush and floss. That is gingivitis. It becomes periodontitis when the inflammation causes separation of the fibers that hold the gum to the teeth the plaque may start to cause a reaction that leads to bone loss.

Stages: Gum disease is the first stage of mouth infection where the bone is not effected. Periodontal disease is later with the infection causing bone loss and more infection. If left untreated be prepared to lose all of your teeth and have a difficult time making a denture fit.