An online panel is a managed database of pre-screened individuals available for internet-based research studies, including surveys, qualitative interviews, and longitudinal tracking programmes. Panel providers recruit, profile, and maintain these participants so that research teams can quickly access audiences matching specific criteria without building their own recruitment infrastructure. In research operations, online panels are a core mechanism for reducing the time and cost of participant recruitment, particularly for studies requiring hard-to-reach segments or multi-market coverage. Panel quality varies significantly across providers, and experienced researchers evaluate panels on fraud controls, profiling depth, engagement rates, and the transparency of how participants were originally recruited and incentivised.