Imagine you have a bunch of toys - blocks, cars, dolls, puzzles. You can play with each of them separately, but what if you wanted to make a new toy by combining them? That's kind of what a mashup is!
On the internet, there are lots of different websites with different features - some show maps, some are for socializing, some have news articles. Each website is like a toy. But sometimes it's helpful to combine different website features to make something new and useful.
A web application is like a toy that you can play with on the internet. A mashup is a special kind of web application that combines parts of different websites. This makes a new web application that has more features than any one of the websites alone would have.
For example, imagine there is a website that shows you how long it will take to get from one place to another using different modes of transportation, like walking or taking a bus. And then there is another website that shows you where all the public bathrooms are in the city. These websites are like toys. But if you mash them up, you could have a new web application that helps find the fastest route to a bathroom!
A mashup is a web application that combines different parts of websites to create something new and useful.