It means it's the numbering from the Atlas of Peculiar Galaxies, by Halton Arp.
Messier
The 'w' on an ARP warden stands for Warden.
He came from bilingual Asace. Speaking French he called himself Jean Arp; speaking German he said Hans Arp. He had no other names.
There are many full forms for ARP. In Military,it is Air Raid Precautions Ref. wikipedia.org/wiki/Air_Raid_Precautions abbreviations.com/ARP
ARP is not an abbreviation, but rather an acronym. It stands for several different things but the most common is Address Resolution Protocol which is used in computer networking.
ar stands for air raid protocal
Air Raid Precaution
Dynamic ARP table entries are created whne a client makes an ARP request that cannot be satisfied by data already in the ARP table.
arp -a show arp
Air Raid Precautions
Probably... well... Air Raid Precautions...
Prlg stand for power ranger lost galaxy.