This is the 79th most frequent German word.
ihn
"Him" (accusative form of "he" in English).
The word 'ihn' is the accusative form of 'er', the third-person singular masculine pronoun, used as the object of the verb 'sehen'.
Ich sehe ihn im Park.
I see him in the park.
'Ihn' here is again the accusative form of 'er', representing the direct object of the verb 'kennen'.
Wir kennen ihn gut.
We know him well.
In this sentence, 'ihn' serves as the direct object of the verb 'lieben', referring to 'him' as the entity being loved by the dog.