Answer:
A mineral reserve is a resource, or a portion of a resource that can be mined profitably. It’s quantity and quality have been demonstrated to the point that there is real certainty that it exists that way. Allowances have been made to include dilution (non-ore rock that is mined with the ore), and mining losses ( you can never mine it perfectly).
A resource is an estimated quantity of a mineral of economic interest, that has potential to be mined economically. It can have less certainty than a reserve.