Opportunity Sampling or Convenience Sampling is a type of Nonprobability Sampling where participants are selected based on naturally occurring groups.
For example, let's say you want to study sharing behavior of preschool children. Instead of taking a random sample of preschool-aged children, you decide to visit your local preschool and select a class of preschoolers as your sample.
Opportunity Sampling is a popular technique, especially among psychology students who may not have the time or money to select a truly random sample. The downside of this method is that you may end up with biased results. In the example given, the sharing behavior of preschoolers in your area may not be representative of the behavior of all preschoolers due to environmental, cultural, or socio-economic factors.