What is the rate limiting step in a chemical reaction?
The rate limiting step is the slowest step of the entire chemical reaction that determines its overall rate.
Here is an analogy for you to better understand.
Imagine driving along a highway and the car in front of you is going at a rate of 100kph. No matter how fast you drive, your rate has been set by the car in front of you, meaning you (ideally) cannot go any faster than 100kph.