An interest rate guarantee (IRG) is an option on a forward rate agreement (FRA) that is handled over-the-counter (OTC).
A call IRG is called a borrower's IRG. A put IRG is called a lender's IRG.
When exercising a borrower's IRG, the holder has the option (but is not obliged) to take a loan with a predetermined amount at a predetermined interest rate (the strike of the option) on a predetermined time period.
When exercising a Lender's IRG, the holder has the option (but is not obliged) to make a loan with a predetermined amount at a predetermined interest rate (the strike of the option) on a predetermined time period.
Of course, the seller has the obligation to fulfill the condition of the option.
References
Interest rate guarantee Wikipedia(Text) CC BY-SA