Lookup Filter "OR" Condition

You just need to use the filter logic. You can click the Filter Logic link to allow you to add OR logic to your criteria

Below the list of "Filter Criteria" is a link that reads "Add Filter Logic..." Once you click that, you'll have the option to create a complex filter logic such as (1 AND 2) OR (3 AND 4) OR (5 AND 6) OR (7 AND 8)