ARES (Amateur Radio Emergency Service) is an emergency response group of amateur radio operators. Hurricane wipes out all the phones, but radios still work. ARES operators help with emergency communications until the phones and internet get fixed.

ARC is American Red Cross.

The ARRL (Amateur Radio Relay League) is the main club of amateur radio operators in the USA. There are lots of facets to amateur radio, not just emergency response. There are contests where people try to make many radio contacts (or long distance contacts, or contacts using a certain range of frequencies, etc.), people that just like to chat (known as rag chewing), and serious researchers that develop new modes of wireless communication that may even make it to commercial products. ARRL supports all licensed amateur radio operators in the USA.

MOU is a memorandum of understanding, basically a business agreement.

TNC is a terminal node controller, it's the box that interfaces your digital object (computer or phone) with your analog radio. Many new/expensive radios have built in digital capabilities, but most radios need an audio input.

My BLT drive on my computer just went AWOL