Simultaneous means happening at exactly the same time as something else. If you pat your head and rub your stomach simultaneously, both hands are moving at once. If two runners cross the finish line simultaneously, they arrive in that precise same moment.

In a video call, people in different cities can see and hear each other simultaneously, even though they're thousands of miles apart. During a solar eclipse, millions of people might look up at the sky simultaneously to watch the moon block the sun.

Sometimes simultaneous events create interesting challenges. Try writing with one hand while drawing with the other simultaneously: your brain has to control two completely different actions at once. Orchestra musicians play their different instruments simultaneously, which is why they need a conductor to keep everyone perfectly together.

The word concurrent means something similar, though it suggests things happening during the same general period rather than at the exact same instant. But when something truly happens simultaneously, there's no gap, no delay, no “one after the other.” It's the same moment, perfectly matched in time.