OpenERP conditions in filters are joined with an AND operator.
But it's possible to add conditions with OR filters using an Advanced Search: if multiple conditions are set inside an Advanced Search, they will be joined with an OR operator.
For example, in Sales » Customers, to filter only Companies from either France or Belgium:
- Open the filter dropdown and select [Company] from the default filters.
- Add an Advanced Filter with [Country is equal to France +or+ Country is equal to Belgium].