Roll drag

Roll drag is the cumulative effect of contango on a fund that must keep rolling near-month futures forward — each roll costs a little, and over months or years that cost compounds into meaningful underperformance versus the spot commodity. USO (crude oil) and UNG (natural gas) carry an explicit roll-drag note in this product's proxy list because their underlying futures curves are frequently in steep contango; physically backed proxies like GLD don't have this issue.