This is the 6046th most frequent Japanese word.
イルカ
Dolphin.
'イルカ' in this sentence refers to the animal 'dolphin'. It is the subject of the sentence.
イルカはとても賢い動物です。
Dolphins are very intelligent animals.
'イルカ' is used to denote 'dolphins' in the context of observing them at an aquarium.
水族館でイルカを見ることができます。
You can see dolphins at the aquarium.
'イルカ' is used to refer to 'dolphins' as the subject of the drawing activity.