A mineral resource is rock that might one day be mined economically. It is a geological statement, not a commercial one.
A concentration of material of economic interest in or on the Earth's crust in such form, grade, and quantity that there are reasonable prospects for economic extraction. Resources are classified as measured, indicated, or inferred based on confidence level.
Resources are the raw inventory a junior is valued on, and they are the number most often quoted in headlines. But a resource has not been shown to be profitable to extract — that only happens when it is converted to a reserve through an economic study. Companies without reserves are, in effect, asking you to underwrite that conversion.
Resources are reported in three confidence categories — measured, indicated and inferred — and the split matters more than the total. A deposit that is 80% inferred is a very different asset from one that is 80% measured, even at identical ounce counts.
Adding measured, indicated and inferred together into a single headline number is common and misleading. Inferred material cannot be used in the economic studies that turn a resource into a reserve.
108 terms have their own page: the definition, why it matters to an investor, where it shows up in practice, and the mistake people make with it.