A "convertibility option" refers to the ability to exchange one thing for another. It means having the choice to convert or change something into something else. Full definition
In addition to providing a level benefit for the period that has been chosen, this plan provides a guaranteed convertibility option. (rootfin.com)
They can even consider one that has a «convertibility option» to convert the policy to a whole life policy if they so choose later down the road. (wholevstermlifeinsurance.com)
This is also known as a convertibility option. (accuquote.com)