Definition: Some types of users are unintentionally left out from the research participant pool
You are designing a cycling tracking app and need to conduct research on cyclists. You decide to interview and observe cyclists in New York City, but you fail to recognize that their cycling behavior may differ significantly from those who live in suburban areas with plenty of hills. You are running the risk that your research insights may not apply to all your target audience.
How to overcome it
Define your target audience and list out key differentiators in terms of their background, behaviors and attitudes. Include people of different characteristics in your sample.