Folkbokföring (population registration)
The registration of where you live, with Skatteverket.
Folkbokföring shows where you are resident. It determines, among other things, which municipality and region you belong to, and therefore where you receive services.
Example
If you move, you need to report your move to Skatteverket.
Why it matters
Having the correct registered address matters so you receive post from authorities — such as a summons to the test.