A non-departmental public body (or NDPB) is a type of organization that works for the government but is not part of a particular government department. It's kind of like a special group of people who are hired by the government to do certain things that don't necessarily fit into a specific department.
NDPBs are set up to carry out specific tasks or provide specialized services, like managing public parks or regulating certain industries. They are given some independence from the government departments in order to carry out their work more effectively. However, they are still accountable to the government and have to follow certain rules and regulations.
So, basically, NDPBs are groups of people who work for the government but are kind of like their own little teams, doing their own special jobs that don't quite fit into a regular department.