i want to know about external key what is these external key which comes after running ccr as manufacturing order missing in r3 with external key

i want to know about external key what is these external key which comes after running ccr as manufacturing order missing in r3 with external key

after seeing log it gives information that order exist only in apo after deleting from in apo it goes away

But i what to know what is these external key

Thanks in advance

Regards

Virender