The borrower's right to void or cancel a loan transaction at no cost to themselves within three days of closing. Right of rescission is not applicable to a mortgage made to purchase a home, only other mortgages such as refinancing or home equity loans.

• Also known as a "cooling off period"
• Note that a right of rescission can be waived under dire circumstances - i.e. a person is an immediate need of the money for medical expenses or something else of an immediate nature. 

Bankapedia's Take

The right of Rescission is one of the more valuable laws that the goverment has enacted regarding mortgages. An unscrupulous loan officer will have several sleepless nights during the time between recscission and close of escrow, as they hope their borrowers won't realize the error of their ways in these three days.

As noted above,  a borrower can elect to avoid the recission period and close immediately, if they are doing a cash out refinance and need the money yesterday. Due cause must be documented and you must sign your rights of recsission away.