An isosbestic point is like when you have two different things and you mix them together, but they turn into something else that looks the same as when you mixed them. It's kind of like mixing paint colors - if you mix red and yellow, you get orange, but if you mix blue and yellow, you also get orange! So even though there were different things mixed together, the end result looks the same.
When scientists talk about an isosbestic point, they usually mean that they're looking at two different things that absorb light (like two paint colors mixing together). They shine a light on the mixture and see how much light is absorbed by each of the things in the mixture. But at the isosbestic point, both things in the mixture absorb light in the same way, so no matter how much of each thing is in the mixture, the amount of light absorbed by each thing is the same. It's like both things are working together to absorb the light equally.
Scientists like to use isosbestic points because they can use this to learn things about the mixture, like how much of each thing is in the mixture or what the mixture is made of. So it's kind of like a secret code that helps them figure out the mystery of what they're looking at!