They are replacement notes, printed separately from the regular printing process, to replace a damaged note or sheet of notes, typically identified by a star ( ) in the serial number.
Because they are not produced regularly, they are a "rare" treat to find in a standard bank teller strap of $1 bills.
Tell you how to check if a star note is from a (using a Star Note Lookup tool).
While many star notes are actually quite common, they become highly collectible and valuable if they come from a low print run (under 3.2 million, or sometimes under 640,000 for extreme rarity), feature fancy serial numbers (like radars, ladders, or solids), or are part of older series currency.
Help you identify the (like Red Seals).
A 2021 series $1 star note with a 3.2 million print run is generally considered face value (common), while others, depending on demand and condition, can carry significant premiums. If you are interested in this topic, I can:
A highly sought-after variant is the filled star error, where too much ink makes the star look solid, increasing its value to collectors due to the printing defect.
Explain the difference between a and a repeater serial number.