Cordyceps mycelium, the same active part of the mushroom, grown sustainably by fermentation instead of harvested from the wild.
These are cultured fungi grown in tanks or on grain, and they are chemically distinct from the wild fruiting body they stand in for. Mycologists at the Chinese Academy of Sciences classify Paecilomyces hepiali as a fungus isolated from wild Chinese cordyceps rather than as that organism, and identify Hirsutella sinensis, not Paecilomyces, as the true asexual form of the wild species. Where the same fungus has been grown both ways, the cultured mycelium and the fruiting body differ substantially in protein, carbohydrate and antioxidant content. On the energy claim specifically, the two best exercise trials of Cs-4 found nothing: no change in maximal oxygen uptake, ventilatory threshold or time-trial performance in trained cyclists over five weeks, and no change on a commercial Cs-4 formula in cyclists over two weeks.
Sustainably grown is doing quieter work than it looks. The word describes a real advantage in cost and supply while sliding past the point that this is a different fungus, grown a different way, with a different chemistry.