Since 1981 the Bureau of Engraving and Printing has sold full-uncut sheets of currency. Originally only small denominations of $1 and $2 were available. But now you see $5, $10 and $20 denomination sheets as well as 16-note $50 sheets.
The uncut sheets have special serial numbers, higher than the serials used on circulated notes. However, uncut sheets of star notes are usually leftovers from regular production runs, rather than special printings for collectors, and so the star sheets do not use high serial numbers.