"If the notes are to be paid from specific taxes due in the near future, they usually are called tax anticipation notes (TANs); if from anticipated intergovernmental revenue, they are called revenue anticipation notes (RANs). If the notes are to be paid from long-term borrowing (e.g., bonds), they are called bond anticipation notes (BANs). Tax anticipation notes and revenue anticipation notes are often grouped together and referred to as tax and revenue anticipation notes (TRANs)."
Found this from an online source. TRAN's are hooked to a specific TAX i.e. I believe Harris County's are tied to the property tax for the coming year. Where Bonds are usually long term and not tied to a specific tax. To the investor I am not sure if there is a difference. I don't know if TRAN's have a tax advantage that bonds do.