A "Digital Repeater" that receives a packet and immediately re-transmits it to extend the signal's range. Modern systems use "New-N" paradigms (like WIDE1-1) to control how many times a packet is repeated.
A station that acts as a bridge between the local RF (Radio Frequency) network and the APRS-IS. It typically receives packets over the air and "gates" them to the internet.
A numeric suffix added to a callsign (e.g., -9 for a primary mobile, -7 for a handheld) to distinguish between multiple devices owned by the same user.
The destination address field in an APRS packet, which is usually used to identify the software or hardware device type rather than a specific recipient.