Citizen Science has been defined many different ways. Two popular definitions are:
"scientific research conducted, in whole or in part, by amateur (or nonprofessional) scientists" - - Wikipedia.
"projects in which volunteers partner with scientists to answer real-world questions" - - Citizen Science Central website
Projects might include collecting or analyzing data, observing and recording natural phenomena, or developing software or instrumentation. Citizen science projects promote public engagement with science and bolster researchers efforts by providing more volunteers and/or computing power. Little knowledge or training is needed to participate in the projects, participants have the opportunity to learn more about science and projects exist for all age groups.