den

This is the 3rd most frequent German word.

den

"Den" is the accusative form of the masculine definite article "the" in German.

Definite article in the accusative singular masculine case.

Ich sehe den Hund.

I see the dog.

Definite article in the dative plural case.

Ich gebe den Kindern das Buch.

I give the book to the children.

Relative pronoun in the accusative singular masculine case.

Den Apfel, den du isst, ist rot.

The apple that you are eating is red.