Bodensee
In short
A large lake located at the border of Germany, Switzerland, and Austria. It consists of three main parts: the Upper Lake, the Lower Lake, and the Seerhein.
In plain words
It is a massive body of water sitting at the foot of the Alps. Three different countries share the lake, and the Rhine river flows through it.
A simple example
A person could swim in the Upper Lake in Germany and then take a boat to reach the Swiss side.
Why it matters
It is a vital source of drinking water and a major hub for tourism and transport in Central Europe. The lake also helps manage the flow of the Rhine river.
Easy to mix up
Do not confuse it with Lake Geneva, which is also a large lake in the Alps but located further west.