Is there a universally agreed metric of what a mobile MAU constitutes? Is there a generally agreed unit of time spent per instance of log in activity, to quali

Is there a universally agreed metric of what a mobile MAU constitutes? Is there a generally agreed unit of time spent per instance of log in activity, to qualify as a MAU? Or just the very act of stumbling into the FB app (somehow), through the myriad ways possible out there, still constitute a MAU? I understand that this does not count (?) API calls (justifiably). All these years in, I just want to assure myself that we are still not in the era of sketchy metrics and non-standard parameters. Thats all.