Q. What is the difference between a parameter and a statistic?
A parameter is a number that describes a population. For example, the true mean age of women in the United States is a parameter. The primary issue with parameters is that they are almost always unknown. To get the true mean age of all women in the United States right now (i.e. the population parameter), you would need to have records of every person in the population.
A statistic is a number that describes a sample. For example, the sample mean age of women in the U.S. calculated from a survey of 1,000 members of that population. The primary goal of collecting sample statistics is to make inferences about the population.