Definite article - Bepaald lidwoord

Dutch has two words for the definite article (English the), namely de and het.

De
is used with common gender nouns (i.e. masculine and feminine nouns) and all plurals.
Het is used with neuter gender nouns.

There are some rules for recognizing which nouns are common gender and which are neuter, but it is easiest to always check the gender of a word (e.g. in a dictionary). One rule is that all diminutives are neuter gender words (for example het stukje = the piece). Knowing the gender of a word is very important, because it has repercussions for the ending of adjectives. For example:

Ik heb een leuke buurvrouw. (buurvrouw is a common gender noun)
I have a nice neighbour.

Ik heb een leuk huis. (huis is a neuter gender noun)
I have a nice house.