Short for Multipoint Microwave Distribution System, also know as Multi-channel Multi-point Distribution System and wireless cable, is another wireless broadband technology for Internet Access.
MMDS channels come in 6 MHz chunks and run on frequencies licensed exclusively by the Federal Communications Commission.
MMDS is a line-of-sight service (see Fresnel Zone definition), so it won't work well around mountains, but it will work in rural areas, where copper lines are not available.
MMDS Overview Information from the Wireless Communications Association.