Numerical characteristics of populations ie parameters are values, usually unknown (and which therefore have to be estimated), used to represent certain population characteristics. Within a population, a parameter is a fixed value, which does not vary.
Found on http://www.cirem.co.uk/definitions.html
Variables not in the data, but in the model (eg. distribution, line of best fit) which describes it, eg. mean, gradient, standard deviation. Found on http://www.encyclo.co.uk/local/20429