Questions & Answers about Urðunin er dýr.
In Icelandic, the definite article is usually attached to the end of the noun instead of standing as a separate word.
- urðun = landfill / disposal / burial (indefinite)
- urðunin = the landfill / the disposal / the burial (definite)
So -in here is the attached definite article.
The basic form is urðun.
In the sentence, it appears as urðunin, which is the definite singular form. So if you were looking it up in a dictionary, you would usually search for urðun, not urðunin.
That matters because adjectives in Icelandic often agree with the noun in gender, number, and case. In this sentence, dýr is describing urðunin, so its form matches a feminine singular nominative subject.