This is the 2047th most frequent Japanese word.
亀
Turtle or tortoise.
The word "亀" is used here to represent turtles in general in a symbolic and cultural context.
亀は長寿の象徴です。
The turtle is a symbol of longevity.
The word "亀" refers to a specific pet turtle owned by the speaker, emphasizing an individual animal.
飼っている亀に毎朝餌をあげます。
I feed the turtle I have as a pet every morning.
Here, "亀" describes a turtle observed in its natural environment, likely referring to a single instance of the turtle.