Treasury notes are Treasury securities that mature in two to 10 years (from the time they are issued). The Treasury issues three types: a new two-year note every month, and new five- and 10-year notes quarterly, in the quarterly refunding.
The 10-year note is the U.S. benchmark, meaning that people look to its yield as a proxy for all U.S. interest rates. Formerly, that honor went to the 30-year bond. But reduced issuance of 30-year bonds has given them scarcity value, making them less reliable as an indicator of how high people think interest rates should be.