Non-probability Sample

Sampling is the use of a subset of the population to represent the whole population. Probability sampling, or random sampling, is a sampling technique in which the probability of getting any particular sample may be calculated. Nonprobability sampling does not meet this criterion and should be used with caution. Nonprobability sampling techniques cannot be used to infer from the sample to the general population. Any generalizations obtained from a nonprobability sample must be filtered through one's knowledge of the topic being studied. Performing nonprobability sampling is considerably less expensive than doing probability sampling, but the results are of limited value.
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a sample in which the chance of an individual within the total population being chosen is not known.

a research sample in which the selection of units is based on factors other than random chance, eg convenience, prior experience or the judgement of the researcher. Examples include; convenience, judgmental, quota and snowball.