APRS stands for "Automatic Packet Reporting System"
APRS is a two-way tactical real-time digital communications system between all assets in a network sharing information about everything going on in the local area.
You can read more about it on the APRS website, www.aprs.org
You can view real-time APRS activity in your area on the www.aprs.fi website.
You can also search for APRS stations, both fixed and stationary (like WX5ELP-1) on this link: