Imagine you are playing a game of follow the leader with your friends. The leader is the person who tells everyone else what to do and when to do it. In the game of follow the leader, if the leader says "jump," everyone else jumps.
A slave clock is like the person who is following the leader in the game. It is a clock that listens to another clock, which we call the master clock. The master clock is the leader, and the slave clock does exactly what the master clock tells it to do.
The master clock and the slave clock are usually connected by wires or radio waves so that they can communicate with each other. When the master clock says "tick," the slave clock listens and also says "tick" at the same time. This way, both clocks are always showing the same time.
Slave clocks are often used in places like schools or office buildings, where it's important for everyone to be working on the same schedule. The master clock is usually in one central location, and it sends signals to all the slave clocks in the building to keep them synchronized.
In summary, a slave clock is like a follower in the game of follow the leader. It listens to another clock (called the master clock) and does exactly what it is told to do so that it stays in sync with the master clock.