Quota Sample (The Penguin Dictionary of Mathematics (3rd edition)):
A sample in which the units are not selected randomly but the interviewer is told to choose a certain number of units in each of a number of categories, e.g. 30 women, 16 men, half of each to be over 40, etc. The method is widely used in opinion polls and market research. While sampling error cannot be estimated, a well-designed quota sample often has low sampling error. There is a danger of bias being introduced by interviewer choice, but the prime difficulty in interpreting results of opinion polls, whatever method of sampling is used, often arises from ‘don’t know’ responses and people changing their minds between the opinion poll and the event to which it relates, e.g. a forthcoming election.’
Quota Sampling (Oxford Study Mathematics Dictionary):
Quota sampling is done by deciding in advance how many of the population, in each of certain categories, are to be chosen. The quotas are often set to represent how many of each category are known to be present in the total population.
Example: A survey abut attitudes among older persons might specify that, from the over-sixties, 100 men and 125 women are to be questioned.