When it snows, each individual bit of snow you see is a snowflake. Each snowflake is made up of an ice crystal—or several ice crystals stuck together.
At the center of every snowflake is a tiny particle of dust, which attracts drops of water that freeze and form crystals. If you look at a snowflake through a microscope, you can see how complex its pattern is—and each one really is different from every other snowflake. This fact led to the informal, derogatory meaning of this word, "someone who's overly sensitive because they're supposedly so special."