When repeating an experiment many times and under the same circumstances, such as throwing dice, you are conducting a chance experiment. A possible outcome is $5$ pips.
The relative frequency of that outcome is $\frac{\text{the number of occurrence of that outcome}}{\text{the number of repititions of the experiment}}$ .

According to the law of large numbers this relative frequency approximates a certain number (when the chance experiment is repeated an infinite number of times).
This number is called the empirical probability of this outcome.

Relative frequencies can also be calculated using statistics. This bar diagram shows the relative frequencies when throwing a die $600$ times. It was generated by simulating the throwing of the die with a graphic calculator.

The empirical probability of $5$ pips is approximately $\frac{104}{600}$.