Off-The-Run Treasuries

What Does Off-The-Run Treasuries Mean?
All Treasury bonds and notes issued before the most recently issued bond or note of a particular maturity. These are the opposite of "on-the-run treasuries".

Investopedia explains Off-The-Run Treasuries
Once a new Treasury security of any maturity is issued, the previously issued security with the same maturity becomes the off-the-run bond or note.

Because off-the-run securities are less frequently traded, they typically are less expensive and carry a slightly greater yield.