The natural resources used by society are limited by various factors. why is coal considered a nonrenewable resource?

Coal is considered to be a non-renewable resource because if we use it a lot, we can actually run out of it: it's limited and will not be replenished (unlike for example solar energy which does not face this problem). Actually, it can be replenished through the same mechanism in which it happened, but this cannot happen within a human life-time, which is what people assume when they mean "non-replenishable".