Imagine you are standing on the Earth like a tiny ant. The Earth is a big round ball that spins around and around. As the Earth spins, it has an imaginary line that goes around the middle, which is called the equator. The equator is where the weather is usually warm and tropical.
Now, imagine drawing another line around the Earth, but this time it goes around the top and the bottom part, like a big circle. This line is called the Polar Circle. It is located about 66.5 degrees north of the equator, which means it's pretty close to the North Pole.
Since the Polar Circle is so far away from the equator, the weather and climate are very different. It is usually much colder and there is more snow and ice. In fact, in some places near the polar circle, it can be dark for many months during the winter and then light for many months during the summer!
So, that's what the polar circle is - a big line that goes around the Earth near the North Pole and marks the boundary between places that have very different weather and climate.