This is a word that describes anything about or coming from the sun — Earth’s own personal star. The solar system is the group of planets, including Earth, that orbit the sun. The energy that comes from the sun and fuels all life on Earth — and provides some of our electricity, too — is solar energy. The 365 days it takes for the Earth to go around the sun is a solar year. And when the moon gets between the sun and the Earth, blocking the sun’s light and casting a huge shadow, we call it a solar eclipse.
Why do we say “solar” for sun-stuff instead of something like, er, “sun-er”? Because the word solar comes from the Latin word for sun: sol.