This is the 129th most frequent Icelandic word.
sveitarfélagsins
"The municipality's" (possessive form).
Here, 'sveitarfélagsins' is used in the genitive singular to indicate possession, meaning 'of the municipality'.
Forseti sveitarfélagsins bauð íbúa velkomna á fundinn.
The mayor of the municipality welcomed the residents to the meeting.
In this case, 'sveitarfélagsins' again occurs in the genitive singular to show that the policy belongs to 'the municipality'.
Við ræddum stefnu sveitarfélagsins um umhverfismál.
We discussed the municipality’s policy on environmental issues.
This usage shows 'sveitarfélagsins' in the genitive singular form, describing ownership of the concert by 'the municipality'.