It's a low power, low range radio transceiver. Meshtastic networks are being set up for local communication. Each radio is a node on the network, so in theory as more people join the network, the range will expand beyond line of site. You connect your radio to your phone through bluetooth. It substitutes for a cell or internet connection.

I'm no expert. I may have got things wrong. More knowledgeable people can explain it better.

I'll make a more detailed post when I learn more and get up and running.