Academic: In the academic world a letter of intent is known as a Statements of Purpose and is part of the application process. Real estate: Often times there are properties that are not listed on the MLS or with a realtor. It is at these times that a letter of intent can be used to let the owner of the house know that a potential buyer exists and thus the process of buying and selling the house may begin.
If the letter of intent is accepted, then the due diligence period will begin. It will continue until the time agreed upon by both parties in which, at the end of the term, a binding contract is constructed. Terms may change during this time if certain aspects of a property, previously not disclosed, are discovered.