resistance
Resistance is how strongly a material fights the flow of electric current — the electrical equivalent of friction. Picture water pushed through a pipe: a wide, smooth pipe lets it gush, but pinch the pipe and the same push delivers only a trickle. Resistance is that pinch. It is measured in ohms, and the more a wire resists, the less current a given voltage can drive through it.
Where does the held-back energy go? It turns into heat — which is exactly how a toaster, a kettle, or an old-style light bulb works, deliberately using high resistance to warm up or glow. How much a wire resists depends on its material (copper resists little, nichrome resists a lot), its length (longer means more), its thickness (thinner means more), and its temperature (most metals resist more when hot). Thin, long, hot wires are the stubborn ones.
Resistance is measured in ohms (symbol Ω, the Greek letter omega), named after Georg Ohm, who in 1827 published the tidy rule linking voltage, current and resistance: V = I × R. A common confusion: more resistance does not always mean more heat — run on the same voltage, a higher-resistance device actually draws less current and can give off less heat (power equals V²/R), which is why the math, not intuition, has the final say.