Anyone can be a citizen scientist, regardless of where they are from. It does not matter how old they are or what their background is. All it takes is some time, curiosity, and a sense of wonder.
Even if in a citizen-science project participants are typically engaged in collecting data, for example data about species presence through an app, they can play a role in any of the following phases of a project:
(Projects use many words to describe the people who take part in their activities: citizen scientists, volunteers, stakeholders, amateurs, community members, human sensors. Here we just use the word participants.)