Linked from
The 35 pages that link to Simple harmonic motion, each with the reason it gives.
Harmonic oscillatorBroader topic: It is the motion produced by an ideal harmonic oscillator.
DisplacementBroader topic: Displacement from equilibrium determines the restoring acceleration.
OscillationBroader topic: It is the ideal pattern produced by a linear restoring force.
Periodic orbitBroader topic: Its sinusoidal trajectories are elementary periodic orbits.