In general, the power of a statistical test of some hypothesis is the probability that it rejects the null hypothesis when that hypothesis is false (ISI).
The property of the set of measurements of being very reproducible or of an estimate of having small random error of estimation. Precision is to be contrasted with accuracy, which is the property of being close to some target or true value. Precision is a quality associated with a class of measurements and refers to the way in which repeated observations conform to themselves; and in a somewhat narrower sense refers to the dispersion of the observations, or some measure of it, whether or not the mean value around which the dispersion is measured approximates the "true" value. OECD Source: The International Statistical Institute, "The Oxford Dictionary of Statistical Terms", edited by Yadolah Dodge, Oxford University Press, 2003.
A probability sample is a sample selected by a method based on the theory of probability (random process), that is, by a method involving knowledge of the likelihood of any unit being selected. OECD Source: United Nations Statistics Division, "Handbook of Vital Statistics Systems and Methods, Volume 1: Legal, Organisational and Technical Aspects", Studies in Methods, Series F, No. 35, United Nations, New York, 1991.
Any method of selection of a sample based on the theory of probability; at any stage of the operation of selection the probability of any set of units being selected must be known. It is the only general method known which can provide a measure of precision of the estimate. Sometimes the term random sampling is used in the sense of probability sampling. OECD Source: A Dictionary of Statistical Terms, 5th edition, prepared for the International Statistical Institute by F.H.C. Marriott. Published for the International Statistical Institute by Longman Scientific and Technical.
A sample in which the individual units are selected by some purposive method. It is therefore subject to biases of personal selection and for this reason is now rarely advocated in its crude form (ISI).
Power
