This is the 415th most frequent Icelandic word.
bestu
"Bestu" means "best" in English (feminine plural or definite form in Icelandic).
In this sentence, 'bestu' is used as an attributive modifier to describe the noun 'vinir' ('friends'). It is in the superlative form, declined to agree with the plural definite noun.
Þetta eru bestu vinir mínir.
These are my best friends.
Here, 'bestu' is in the superlative form and agrees with the singular feminine noun 'myndina' ('picture') in definiteness and case.
Hún valdi bestu myndina í keppninni.
She chose the best picture in the competition.
In this sentence, 'bestu' acts as a pronoun referring to 'the best ones,' used in a generic or collective sense. It is plural and matches the implied subject.