Hi gailtravels,
Apologies for not being clearer. An optional booker is a traveller who is waiting on confirmation for an element of the tour that we have to request. For example, this could be a room or flight upgrade or an insurance query. Until we have confirmation of this, they are provisionally booked on the tour. If we don't manage to fulfil the request, we will offer them an alternative or return the deposit.
I hope this makes sense.
Kindest regards,
Monty