A convertible note (otherwise called convertible debt) is a loan from investors that converts into equity. It’s a common way for investors to invest in early stage startups, particularly ones that are pre-valuation.
An investor loans a startup a certain amount of money, but instead of expecting their money back in the form of payments with interest, their “payment” comes in the form of equity.
That conversion from the balance of the loan to preferred stock happens at a specified point — usually a new valuation at the conclusion of a new funding round.
When a company accepts investment in the form of a convertible note, notes are issued instead of priced equity.