This is the 1254th most frequent Swedish word.
nedre
"Lower" or "bottom."
In this sentence, "nedre" is used as an adjective modifying "hyllan" (the shelf) to specify its relative position, meaning the shelf located lower than others.
Den nedre hyllan innehåller kokböcker.
The lower shelf contains cookbooks.
Here, "nedre" functions as an adjective describing "lägenheten" (the apartment), indicating its physical location as being below other apartments.
Jag bor i den nedre lägenheten.
I live in the lower apartment.
"Nedre" in this context specifies the corner of the painting situated at a lower position, modifying "hörnet" (the corner).