Open Data is managed data that is openly accessible, exploitable, editable and shared by anyone for any purpose, even commercially. Open Data is licensed under an open licence.
FAIR data is not necessarily open. Access can be restricted (e.g., following a business model) but there are good reasons why the corresponding metadata should be open.
More on Open Data:
Licensing and sharing (EERAdata Community Platform)
Open Data Essentials (World Bank)
Open Data Commons (Open Knowledge Foundation)