This is the 3463rd most frequent German word.
klein
Small.
Here, 'klein' is used as an adjective describing the noun 'Haus', indicating its small size.
Das Haus ist klein.
The house is small.
In this sentence, 'klein' is used within a descriptive adjective phrase ('kleine Hund') indicating the size of the dog.
Der kleine Hund läuft durch den Park.
The small dog runs through the park.
Here, 'klein' is part of the descriptive phrase ('kleinen Stadt') referring to the relatively small size of the town.