
Perinatal brachial plexus palsy (PBPP) also obstetric brachial plexus palsy, is flaccid paresis of the arm that occurs at birth with a range of motion that is more passive than active.
‘Erb palsy’ falls under one of the categories of PBPP. The classifications are upper, middle, lower or complete.
Reference;
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2435328/