Why Amateur mesh networking (Broadband-Hamnet, AREDN) takes inexpensive consumer Wi-Fi routers and reflashes them with amateur firmware so they operate on the parts of the 2.4 GHz and 5 GHz bands that overlap amateur allocations (13 cm and 5 cm). Running under Part 97 instead of Part 15, hams may use higher power and high-gain directional antennas, and each node automatically finds and routes through its neighbors to form a self-healing data network. The result is a local high-speed IP network carrying file transfer, video, VoIP and messaging without the internet.
Watch out The internet linking description fits systems such as IRLP, EchoLink or DMR talkgroups, which tie repeaters together over the public internet rather than building a radio-only routed data network.
Mesh = hacked Wi-Fi routers on ham bands. Think Broadband-Hamnet/AREDN, not DMR and not the internet.