Nick Hi! Liability insurance ("aansprakelijkheidsverzekering" in Dutch) is insurance that compensates damage for which you are legally responsible. This can be damage you cause to people or to other people's property. Some damages are excluded from your liability insurance and will not be compensated. For example intentional damage or damage caused with a motor vehicle.
Liability insurance is not compulsory in the Netherlands, but it can be useful and the monthly costs are fortunately low.
Normally you take a liability insurance at an insurance company, such as (to name a few) United Insurance, FBTO, InShared, Centraal Beheer, Aon, Ditzo, HEMA, Univé, AEGON or Nationale Nederlanden.
It is true that some banks also offer this, such as ABN AMRO and Rabobank. However, Bunq does not offer insurance.