This is the 1st most frequent Dutch word.
de
"The" (definite article).
The word 'de' serves as the definite article for the plural noun 'bomen' (trees), applicable to all plural nouns regardless of gender in Dutch.
De bomen in het park zijn oud.
The trees in the park are old.
Here, 'de' is used as the definite article for the noun 'kat' (cat), which is a common gender noun, and for 'mat' (mat), which is also common gender.
De kat slaapt op de mat.
The cat sleeps on the mat.
In this sentence, 'de' is the definite article for both 'leraar' (teacher) and 'les' (lesson), emphasizing their status as specific entities in context.