Standing Wave
Definition
A wave pattern that appears frozen in place — with still points (nodes) and wildly vibrating points (antinodes) — formed when two identical waves travel in opposite directions.
Technical definition
The superposition of two counter-propagating waves of equal frequency and amplitude, producing stationary nodes (zero displacement) and antinodes (maximum displacement) at fixed positions. Only certain wavelengths fit the boundaries, giving quantized modes.
Example
Pluck a guitar string: it vibrates as a standing wave with still nodes at the two ends and a big antinode in the middle. Touch the string lightly at its midpoint and you force a node there — the pitch jumps an octave because only half the wavelength now fits.
A standing wave is not a wave that stopped moving. Energy still sloshes back and forth between kinetic and potential forms; it is only the pattern of nodes that stays put. Students who think 'standing' means 'frozen' cannot explain how a guitar string keeps sounding — the string is very much in motion at every antinode.