What is letter of intent?

Letter of Intent: a written document stating that a customer agrees in principle to purchase aircraft from a manufacturer at a given price and for a given quantity, sometimes including an approximate delivery schedule. However a deposit has not been paid and the buyer has not fully committed to the purchase as they are still able to walk away from the deal. Thus the manufacturer cannot guarantee the delivery slots until the finer details of the purchase agreement are negotiated and agreed upon. Once the purchase agreement is signed and a deposit paid, the LoI is converted to a Firm Order.