Statistics - a branch of mathematics concern with the collection, summary of , description of and inference of data or observations or results of an experiment.
also statistics - a number representing a numerical property of a sample of a population

Descriptive statistics - that area of statistics that involves collecting, summarizing and describing data or observations or results of an experiment.

Inferential statistics - that area of statistics concern with making conclusions or judgment (inference) based on analysis of data.

Parameter - a number representing a numerical property of a population, e.g. Mean, median, variance; also called a statistics when the numerial property is made from a sample of the population.

Sampling

Population - the collection of all members or elements of a group of interest.

Sample - a collection of a portion of the population, a sample involving all members of a population is called a Census.

Random sample - a sample obtained from the population in which every member of the population is equally likely of being selected.

Stratified sample - is sampling taken from subgroups (strata) of a population, each subgroup is called a stratum.

Cluster sample - sampled obtained from the grouping of many strata (subgroups).

Systematic sample - samples taken at prescribed intervals usually start at some random point along an ordered list.

Sample of convenience - a sample taken because of its easy availability (convenience) often not taken at random.

Bias - an inclination or preference, especially one that interferes with impartial judgment: prejudice.  Webster's II

Response bias - occurs when results are obtained falsely either by the respondents (sample) or the process or methods used to obtain the results

Nonresponse bias - occurs when segment or portions of the population are inadequately represented.

Experiments

Treatment - a property or characteristic being studied

Treatment group - the group being studied having the property being studied

Control group - the group being studied not having the property being studied

Experiment - any activity design to study outcomes , results, possibility of chance.

Controlled experiment - an experiment in which subjects given treatment is controlled.

Observational study - an experiment where administration of treatment to subject is not controlled.

Randomly controlled experiment - an experiment where subject assigned treatment randomly.

Confounding factor - is a property other than the treatment that can influence the results of an experiment or study.

A double-blind study - an experiment in which neither the subjects nor those conducting the experiment know which subjects are in the control group or treatment group.

A cross-sectional study - different subjects are compared at he same time

A longitudinal study - the same subjects are compared with themselves over different periods of time.