# Confusion between PSK and QPSK

What is the difference between PSK (Phase Shift Keying) and QPSK (Quadrature Phase Shift Keying)? Doesn't PSK need quadrature component for its working?

QPSK modulation is a PSK modulation with exactly 4 constellation points. The constellation points for QPSK are normally at $\left(\pm\dfrac{1}{\sqrt{2}}\pm\dfrac{1}{\sqrt{2}}j\right)$