Notes are auctioned at 2, 3, 5, 7 and 10 years. Unlike treasury-bill, they carry a coupon set close to the market yield at auction, so they price near par on issue and then drift with rates.
The 10-year note is the reference rate for mortgages, corporate borrowing and equity discount models. When a headline says "yields rose today", it almost always means the on-the-run 10-year. Its liquidity is enormous and its futures contract is one of the most traded in the world.
Example: a new 10-year note is auctioned with a 4.125% coupon at a price of 99.62, giving a yield-to-maturity of 4.17%. On $1,000,000 face you pay $996,200 and collect $20,625 every six months.
Related: treasury-bill, treasury-bond, on-the-run, treasury-futures, twos-tens