Nov 7 (Reuters) - The debate over U.S. healthcare reform is full of terms familiar to lawmakers and lobbyists but often obscure to the public.

Here is a glossary of words and phrases being bandied about as Congress takes up President Barack Obama's top domestic priority: a bill that reins in healthcare costs, expands coverage to millions of uninsured people and bars insurers from denying coverage for pre-existing conditions or dropping coverage for the sick.

* Age rating:

This refers to the ratio of how much insurers can charge older people relative to what they charge young people for health insurance. It is particularly important to the AARP, the influential advocacy group for older people. The House of Representatives bill, which is backed by AARP, has a ratio of 2:1, meaning insurers can charge an older person twice what they charge a young person. The Senate Finance Committee bill has a ratio of 4:1, which would allow insurers to charge up to four times for older people what they charge younger people. The AARP prefers that all ages be treated the same for premiums.

* Bending the cost curve:

U.S. healthcare spending is rising much faster than the general rate of inflation. Lawmakers have no expectation of actually cutting prices. The best they hope for is slowing the rate of growth and thus "bending the cost curve."

* Cadillac health plans:

These are high-cost insurance plans that require little or no out-of-pocket expenses for medical treatment. Many union employees, workers in high-risk professions and corporate executives have them. The Senate bill calls for imposing a tax on such plans, something ardently opposed by unions, which are a key Democratic constituency.

* Cooperatives: