A p-value is a numerical value that represents the likelihood that a given result occurred by chance. In other words, the p-value is a measure of how likely it is that a given result would have occurred if the null hypothesis were true.
For example, imagine you are testing whether or not a coin is fair. The null hypothesis would be that the coin is fair, and the alternative hypothesis would be that the coin is not fair. If you flip the coin 10 times and get 5 heads and 5 tails, then you would calculate a p-value to determine how likely it is that this result occurred by chance.