A sampling method in which the members of the sample are not representative of the population, such that some members of the population have a higher or lower probability within the sample which is indicative that not all members of the population are sampled
A biased sample is a non random sample and the can lead to misleading data conclusion
In the question, the sampling of student opinion about the school cafeteria among students who are on the lunch line and so prefer the school cafeteria leaves out the portion of the population that get their lunch from alternative sources.
