A couple of terms that differ from card-type to card-type--
-excluded countries (watch out for Ireland, Israel, Italy, New Zealand, Australia, and maybe others, as those are countries excluded by one or more card types)
-maximum value of rental car/excluded makes & models
-max length of rental covered (can differ between domestic/international)
-primary/secondary (all except Diner's secondary in country of residence; some primary outside country of residence)