WhatTwo insulated copper wires, twisted around each other in a spiral. Sounds like a small detail — it isn't.

WhereThe Ethernet cable plugged into your router right now. Also used in telephone landlines.

WhyTwisting isn't cosmetic — when two nearby wires pick up the same outside electrical noise, twisting makes that noise cancel out between the pair, instead of corrupting your signal. Cheap to manufacture, which is why it's the default choice for most short-distance wiring.

WhatA single copper wire down the center, wrapped in insulation, then wrapped again in a braided metal shield.

WhereOlder cable-TV wiring (the thick round cable behind your TV), and some early Ethernet setups.

WhyThat outer metal shield blocks outside interference far better than twisted pair can — so it was the go-to choice when signal quality mattered more than cost, before fibre became affordable.

WhatA strand of glass, thinner than a human hair, that carries data as pulses of LIGHT instead of electricity — the light bounces along the inside of the strand (total internal reflection) all the way to the other end.

WhereThe undersea cables connecting continents, backbone internet links between cities, and increasingly, fibre-to-home internet connections.

WhyBecause it's light, not electricity, no electromagnetic interference in the world can corrupt it. It also loses far less signal over distance than copper, so it can travel thousands of kilometers without needing constant boosting — which is exactly why it's laid across ocean floors instead of copper.

WhatElectromagnetic waves sent through open air, at frequencies that can pass through walls and objects.

WhereWi-Fi at home, FM radio, Bluetooth.

WhyOmni-directional (spreads in all directions), so the sender and receiver don't need to be precisely aimed at each other — perfect for devices that move around, like your phone walking room to room.

WhatHigher-frequency waves that travel in a narrow, focused beam rather than spreading out.

WhereSatellite communication, and long-distance point-to-point links (e.g. connecting two mobile-network towers across a valley).

WhyThe focused beam can travel much further with less power than radio waves — but only if there's a clear line of sight between sender and receiver (a mountain in the way genuinely breaks the link).

WhatLight just below the visible spectrum, used for very short-range communication.

WhereTV remote controls, some short-range device-to-device transfers.

WhyCheap and simple to generate — but completely blocked by walls, which is exactly why your remote stops working the moment you point it away from the TV.