Phase angle is a measure of the position of a particle in simple harmonic motion (SHM) relative to its mean position. It is defined as the angle made by the radius vector of a circle with a horizontal axis, where the projection of this vector corresponds to the particle's displacement. A phase angle of 0 indicates the particle is at its maximum displacement, while a phase angle of 45° (or π/4) indicates the particle is at a specific point in its oscillation. Understanding phase angle helps in analyzing the motion and position of oscillating particles. This concept is essential for grasping the dynamics of oscillatory systems.