"Standard of care" basically means "whatever the current protocol to treat the disease is" (normally it means "the accepted treatment", but there isn't one yet)

"Standard of care" basically means "whatever the current protocol to treat the disease is" (normally it means "the accepted treatment", but there isn't one yet), which can mean just trying to keep the fever down, supplementation of fluids, but also administration of drugs (with the exception of the one tested, of course). As you can imagine, it is quite variable in what it means, because it varies across countries and occasionally even hospitals (I'm sure the RECOVERY people have taken this into account, though). It is different from a placebo study because in that case your control is something you know is inert and "does nothing".