Why is the bar pendulum called compound pendulum?

Hint: A pendulum is a weight that is suspended from a pivot and can freely swing. When a pendulum is displaced sideways from its resting, equilibrium position, gravity acts as a restoring force, accelerating the pendulum back to its equilibrium position. The restoring force acting on the mass of the pendulum causes it to oscillate around the equilibrium position, swinging back and forth, when it is released.

Complete answer:
A compound pendulum, also known as a physical pendulum, is a swinging rigid body that is free to rotate around a fixed horizontal axis. Because a compound pendulum, like a swinging bar, has extended mass, it is referred to as a bar pendulum.The simplest type of compound pendulum is a bar pendulum.

It takes the shape of a rectangular bar with holes spaced evenly along its length.The bar pendulum is made up of a one-meter-long metallic bar. Along the length of the bar, a series of circular holes, each about 5 mm in diameter, are drilled. A horizontal knife-edge passes through any of the holes and suspends the bar.

Note: The most well-known application of pendulums is in clocks. A pendulum is used to tally time in many clocks, most notably the "grandfather clock." The length at which the pendulum is suspended determines the exact intervals at which the pendulum swings back and forth. A pendulum clock must remain stationary in order to accurately measure time. Any sudden movement of the clock disrupts the pendulum's regular motion.