Organizational arrangements and the legal and regulatory framework - the 'enabling environment' - in which organizations operate. More broadly, institutions include entities, processes and linkages between individual entities.
Organizational arrangements and practices through which collective actions are taken (e.g. business, courts, government, religious communities, schools, police, and unions).
Fairly stable social arrangements through which collective actions are taken (e.g., government, business, unions, schools, churches, courts, police).