The economically mineable part of an indicated resource — and usually the larger share of any reserve statement.
The economically mineable portion of an indicated and, in some cases, a measured mineral resource. Probable reserves have a lower level of confidence than proven reserves but are still suitable for mine planning purposes.
Most reserves at most mines are probable rather than proven. That is normal, not a warning sign; requiring measured confidence across an entire deposit would rarely be worth the drilling cost.
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.