A resource is an occurrence of minerals that is believed to have the potential to be technically and economically extracted. The degree of confidence that is held in the estimated quantity, quality and mineability of the minerals is reflected in the different categories assigned to resources – namely ‘inferred’ (the least certain), ‘indicated and ‘measured’ (the clearest indication of expected grade and tonnage).
A mineral reserve is part of a resource that more detailed geological and metallurgical evaluation has shown to be economically mineable. The degree of certainty in this evaluation is given by the categorisation of reserves as either ‘probable’ or ‘proven’. And for more detail click and see wikipedia entry.