The group of individuals used to represent a population is called the sample. It should have the same statistics as the population, though be of a smaller size.
statistics
genetic variation
Bias
population
INFERENCES Any calculated number from a sample from the population is called a 'statistic', such as the mean or the variance.
sample.
statistics
demographics, census data
The number of individuals in the population is the population's size. If a population is small enough you will be able to determine the size by counting the individuals.
immigration
Emigration.
Descriptive statistics give information regarding a data set. For example, any graph, the mean, median, and mode, standard deviation, range, and variance are all descriptive statistics. Inferential statistics is using a representative sample from a population to say something about that population. For example, for presidential polls, not everyone in the country is called and asked who they plan to vote for. Whoever does the surveying picks a sample that should fairly represent the population as a whole, and just asks those people. Depending on the sample size, the surveyor can then determine how accurate the results are, and use them to generalize to the population as a whole.
Over population.
genetic variation
emigration
dispersion
Moving out of a population is called emigration. (Moving into a population is called immigration.)