Node (Wave)
Definition
A point on a standing wave that never moves — where the two traveling waves always cancel out.
Technical definition
A point of zero displacement (and zero amplitude) in a standing wave, occurring where incident and reflected waves interfere destructively at all times. Adjacent nodes are separated by half a wavelength (λ/2).
Example
On a guitar string, the ends are nodes — they cannot move. Touching the string lightly at its midpoint creates a node there, forcing the harmonic an octave up.
Common confusion
Nodes are points of zero motion but maximum pressure variation (in sound waves). ‘Nothing happening’ at a node refers to displacement only — other quantities like pressure can be at their extreme there.