Coincidental describes something that happens by chance or accident, without being planned or caused by anyone. When two things seem connected but actually aren't, they're coincidental.

Imagine you're thinking about your friend Sarah, and right at that moment, she calls you. That's a coincidence: your thoughts didn't cause her call, it just happened at the same time. Or maybe you wear your lucky red shirt to school and ace a test that same day. The good grade and the shirt are coincidental: the shirt didn't cause your success, even though they happened together.

Coincidental events can feel surprising or even a bit mysterious, but they're really just the result of random timing. If you and your classmate independently choose the same topic for your reports, that's coincidental. If you run into your teacher at the grocery store, that's a coincidental meeting.

Scientists and mathematicians use the word to be clear when two things happen together purely by chance, not because one caused the other. Understanding what's coincidental helps you think clearly about cause and effect. Just because two things happen together doesn't mean one caused the other.