when the u s treasury issues securities treasury notes and bonds it does so through an auction process to determine the price at which these debt instruments will be offered based on the bids received and the level of interest shown for the security the u s treasury is able to set a price for its debt securities the new issues presented after the auction is closed are referred to as on 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 
for example if the u s treasury newly issued 5 year notes in february these notes are on the run and replace the previously issued 5 year notes which become off the run in march if another batch of 5 year bonds is issued these march notes are on the run treasuries and the february notes are now off the run and so on 