Most banknotes are printed on sheet-fed machines. That is, big sheets of paper are fed into a the machines where the images are printed. The sheets can have 32, 40 or even 50 banknotes per sheet. Some countries sell uncut sheets of banknotes to the collector market. Some collectors like to collect these and frame them as art. Banknote World carries these sheets from a number of countries.
Single banknotes are works of art. Multiple rows and columns of the same piece of art, makes for a new symmetric piece of art. Andy Warhol made many pieces of art in this style showing a famous person over and over again. Uncut sheets are a bit like this. Uncut sheets of Oman Rial are some of the most beautiful and rare pieces of art. Alone the colors and portrait of the former Sultan jump off the page. Having an sheet of 2, 4, 8 or even 32 Rial paper banknotes turns into nice art. Tonga, Samoa and Ukraine also have very attractive uncut sheets, while the Mexico 20 peso is a polymer-based.
One of the most common country to collect uncut sheets from is the United States. The US Bureau of Engraving and Printing have made available uncut sheets of all its denominations- even the USD$100. As you can imagine a sheet of 40 $100 bills is pretty expensive. The most common are either the $1 and $2 dollar sheets of 4 or 5 banknotes. They are inexpensive and are not too big. Who says art is expensive?