Convertible notes are a founder friendly way to fund a seed round

A convertible note is an investment vehicle often used by seed investors investing in startups who wish to delay establishing a valuation for that startup until a later round of funding or milestone. Convertible notes are structured as loans with the intention of converting to equity. The outstanding balance of the loan is automatically converted to equity at a specific milestone, often at the valuation of a later funding round. In order to compensate the angel investor for the additional risk of investing

Source: Convertible Notes | FundersClub