Parameter and statistic both are descriptions for groups. The difference between them is the type of group that each describes. Parameters describe populations. Statistics describe samples from some of the population.
An example of a parameter is 100 students voting whether to have recess on a rainy day or not. 10% of the students voted to not have recess. Being that we know there are 100 students, we can identify the vote of every student. On the other hand, statistics will not give an exact amount of how many people are being referred to.
For example, if one says 70% of Americans prefer Pepsi over Coke, we would know this is a sample because it is not possible to poll all Americans on what type of soda they like.