'By ‘public’ we mean everyone in Ireland who has an interest in health and social care as a public service including potential users of services. By ‘patient’ we mean people who use services such as patients, service users, clients or their carers'

'By ‘involvement’ we mean the active involvement between people who use services, carers, the general public and researchers'

'It does not include the use of people as participants in research (or as research ‘subjects’) and does not provide data for individual research projects'

• Participation: The recruitment of study participants is participation of the public;
• Engagement: Efforts aimed at raising awareness among the public around research, such as media publications, outreach activities such as open days in research facilities can be described as engagement. Engagement activities are required for both participation and involvement;
• Involvement: refers to co-created and co-produced research with a focus on collaboration.

occurring when individuals meaningfully and actively collaborate in the governance, priority setting, and conduct of research, as well as in summarizing, distributing, sharing, and applying its resulting knowledge. 

It is also useful to include the often-quoted definition of PPI developed by INVOLVE, an English organisation which supported PPI in research, which has now been replaced by the Centre for Engagement and Dissemination: 

PPI is research carried out ‘with’ or ‘by’ patients/members of the public rather than ‘to’, ‘about’ or ‘for’ them.