The term IOUS is an acronym for 'I Owe You Something'. It is commonly used to refer to a debt or obligation that one person owes to another. NOTES, MARKERS, debts, and CHITS are all forms of IOUs. NOTES are written promises to pay a certain amount of money at a certain time. MARKERS are similar to NOTES, but are usually issued by banks or other financial institutions. Debts are amounts of money owed to another person or entity. CHITS are informal IOUs, usually between friends or family members.