All the vehicles I have bought in the USA have had clear titles or clear for several years. My understanding of their banking system, is a title that shows a lein on it is similar to our chattel mortgage system.
When a bank/credit union/ect here finances a vehicle they register a chattel mortgage against the vehicle (this might vary by Province). This gives the bank first claim on the vehicle until the chattel is payed off.
chattel mortgages:
What Is A Chattel Mortgage
In the USA a "lein" is placed against the vehicle and this is recorded on the title (usually on the back side). It states the date, amount and who is owed.
So a lein release form would come from the financial institution that lent the money shown on the title.
It should basically state that the loan was payed off on such and such date and they no interest in the vehicle and would be on their letterhead.
Sample form:
Release of Lien Free Form
If the title is clear of leins then no release form would be needed.