Parameters are the unknown values of an entire population, such as the mean and standard deviation. Samples can estimate population parameters but their exact values are usually unknowable.

Parameters are also the constant values that appear in probability functions. These parameters define the shape of probability distributions. Parameters are typically denoted using Greek symbols to distinguish them from sample statistics.

For example, the parameters of the normal distribution are μ ( mu = population mean) and σ (sigma = population standard deviation).