The Open Market Option (sometimes abbreviated to OMO) is the right you have to buy your annuity from any provider. You do not have to buy your annuity from the company you have been saving with; although it might be easiest to do so, you should bear in mind that you might get much better value from another provider.
if you are a member of an occupational pension scheme, you may find that the trustees will carry out an open market option search on your behalf. In other circumstances, you will probably need to take financial advice. But read the Regulator's guide first.