Okay, so think about when you've been outside on a hot, sunny day. Sometimes it feels really hot and sticky, like you're sweating a lot and your skin feels wet. That's because of something called humidity, which is how much moisture is in the air around you.
Humidex is a way of measuring how hot and humid it feels outside, based on a combination of the actual temperature and how much humidity is in the air. It's like a number that tells you how uncomfortable you might feel if you're outside for a long time.
So let's say it's 30 degrees Celsius outside, which is already pretty hot. If the humidity is really low, like only 10%, it might feel pretty comfortable because the air is dry. But if the humidity is really high, like 90%, it's going to feel a lot more uncomfortable because the air is really wet and sticky.
Humidex takes all of these factors into account to give you a better idea of how hot and uncomfortable it's going to feel outside. It's a way of warning you that even though the actual temperature might not be that high, it's going to feel a lot hotter and stickier because of the humidity. So always pay attention to the humidex, especially on hot summer days, and make sure to stay cool and hydrated!