Elementary Statistics (1+1)

3.1.7.2 Non-probability Sampling 

Non-probability sampling methods are those which do not provide every item in the universe with a known chance of being included in the sample. The selection process is, at least, partially subjective.

It may be noted that the term random sample is not used to describe the data in the sample but the process employed to select the sample. Randomness is thus a property of the sampling procedure instead of an individual sample. As such, randomness can enter processed sampling in a number of ways and hence random samples may be of many kinds.