This twenty dollar bill is what we call a legal tender note or a United States note. The design type was used for 1869, 1875, 1878, and 1880. This is not a very popular issue. The design is not especially attractive. The major issue is that it was used for so long that even the rare varieties are not exciting because you can buy something that looks 99.9% the same for a fraction of the cost. In fact, some notes from the series of 1880 were still being printed as late as 1910. 1910 is the first year star notes were issued; and some 1880 $20 bills do exist as star varieties.
Unlike most dealers, we do pay premiums for all legal tender notes as pictured above. Please give us a chance to make an offer on your $20 bill.