What is epoch?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The term "epoch" is often used in the context of oscillations and simple harmonic motion (SHM). To understand what an epoch is, we need to relate it to the motion of a particle.

2. **Circular Motion Analogy**: Consider a particle moving in a circular path. The motion of this particle can be projected onto a straight line, which represents simple harmonic motion.

3. **Defining Initial Phase**: In SHM, the position of the particle can be described using a sinusoidal function. The initial angle or position of the particle at time \( t = 0 \) is referred to as the initial phase.

...