A trader that sells (writes or issues) an option contract to a market participant, assuming the obligation (i.e., standing ready) to buy or sell the underlying (of the option) if the option holder exercises the option. Upon exercise (in the case the option is in the money, ITM, for the holder), the grantor may be required to settle in cash or deliver the underlying physically to the option holder.

It is also known as an option writer or option seller.