Fidonet is an international amateur network of computer systems, often running public access bbs's, and all connected by modem (& often via the internet as well). "Othernets" are distribution networks which use fidonet software. Also known as Fidonet Technogy Networks (FTN).
FidoNet: Technology, Use, Tools, and History, By Randy Bush
"Fido", "Fidonet", and the dog-with-diskette were U.S. registered trademarks of Tom Jennings, firstname.lastname@example.org, but that has since lapsed.