Symmetry is a big, fancy word that describes when things look the same on both sides. For example, if you were to cut a picture of a butterfly in half down the middle, both halves would look pretty much identical.
Symmetry happens all around us in nature - in the shapes of flowers, the wings of birds, and the shells of snails. Even the human body has some symmetry, like our two arms and two legs that are nearly identical.
Sometimes the symmetry is really obvious, like when a snowflake has six tiny arms that are all the same. Other times, it's more subtle, like when you look at the stripes on a zebra. No matter where you look in nature, there's always some kind of symmetry to find!