What does “deductible” or “excess” mean ?

A deductible is the amount that will not be refunded to you regardless of your expenses.
Example: You go to the dentist and this consultation costs you 75 euros. If your deductible is €30, you will be reimbursed based on the remaining €45. The refund will depend on the contract you have signed up and will be able to cover either all or part of the remaining 45 euros.