If you take out a loan, mortgage or phone contract, for example, with BKR, it will be registered and recorded with BKR. This is a neutral or 'positive' registration. The moment you default on your payment obligation for an extended period of time, the registration changes to a negative BKR registration.
A negative BKR registration means that in many cases you cannot take out new credit, think about applying for a (new) loan, taking out a lease or a new phone.
Here's how to avoid a negative registration and what you can do to get rid of a negative registration.