A Participant with fewer opportunities is 

People with fewer opportunities means people who, for economic, social, cultural, geographical or health reasons, a migrant background, or for reasons such as disability and educational difficulties or for any other reasons, including those that can give rise to discrimination under article 21 of the Charter of Fundamental rights of the European Union, face obstacles that prevent them from having effective access to opportunities under the programme.

_{Source: Erasmus+ Programme Guide Online, Glossary}

In Beneficiary projects, check the Participant with fewer opportunities flag to indicate that a participant in an activity (i.e. mobility activity, group activity, participations, events, etc.) is considered a participant with fewer opportunities.