To occur means to happen or take place. When something occurs, it comes into being or takes place at a particular time. A solar eclipse occurs when the moon passes between the Earth and the sun. A funny thought might occur to you during a serious assembly, making you want to laugh at the wrong moment.

The word suggests something happening without someone deliberately making it happen. Lightning occurs during thunderstorms. Your birthday occurs once a year. Scientists study when and where earthquakes occur so they can better understand these natural events.

When an idea occurs to you, it means you suddenly think of it, like when the solution to a puzzle occurs to you while you're doing something completely different. “It never occurred to me” means you didn't think of something at all.

You'll often see occur used with time and place: problems can occur during an experiment, opportunities occur throughout life, and interesting patterns occur in nature.