Frequency-locked loop

A frequency-locked loop is like a buddy system for two things (let's call them Thing A and Thing B) that need to stay in sync with each other. The way it works is that a special device (let's call it the Buddy) watches Thing A closely and keeps track of how often Thing A does something (let's call it Action X).

After some time passes, the Buddy checks in with Thing B and tells Thing B how often Thing A has been doing Action X. If Thing B has been doing Action X at the same rate as Thing A, everything is good and the Buddy doesn't say anything.

But if Thing B has been doing Action X at a different rate than Thing A, the Buddy will tell Thing B to speed up or slow down so that both Thing A and Thing B are doing Action X at the same rate again.

Think of it like two people walking together, but one person gets distracted and starts walking faster or slower than the other person. The Buddy system would check in with both people and tell the faster person to slow down or the slower person to speed up so that they are walking side by side again.

A frequency-locked loop is used in a lot of technologies, like radios and cell phones, to make sure everything stays in sync and works properly.