An HTML application is a way of creating a program that works in a web browser. You know how you use a web browser to visit websites and play games online? Well, an HTML application is kind of like a game or a tool that you can use right in your web browser, without needing to download anything or install any programs on your computer.
When people create an HTML application, they use a special kind of computer code called HTML, which stands for Hypertext Markup Language. This code helps the web browser know what to display on the screen and how to interact with the user.
Sometimes HTML applications are made up of just HTML code, but often they also use other types of code like JavaScript and CSS to make them look and work a certain way. Think of it like a recipe for a cake - you need different ingredients to get the flavor and texture you want.
HTML applications can do lots of different things, like let you type in information and save it to a database, or play a game where you move your mouse around to control an object. They can also look really different from each other, since people can design them however they want using HTML, JavaScript, and CSS.
Overall, an HTML application is like a little program that lives on a website and lets you do things without needing to download anything. It's made using special code that helps the web browser know what to do, and it can look and work in lots of different ways depending on how it's designed.