A natural spring of water, or a constructed fountain. Often used in place names and poetic contexts.
山の中に小さな泉があった。
There was a small spring in the mountains.
公園の泉のそばで待ち合わせよう。
Let's meet by the fountain in the park.
A spring is welling up from within the mountain.
The villagers go to draw water from the spring every morning.
The long drought caused the spring to dry up.