### Virtual DOM React uses the concept of a virtual DOM. It creates a representation of your component hierarchy and then renders those components by creating real DOM elements and inserting them where you tell it ### JSX JSX is a syntax invented for React for function calls that create DOM elements. ### Babel JSX elements compiled down to JavaScript by a tool called Babel. Babel is a compiler that transforms code into valid ES5 JavaScript that all browsers can understand ### Component A component is just a JavaScript function that returns JSX to form a piece of our UI. A function component must return a single element. ### Close Every Element JSX requires that every element be closed, similar to XML or XHTML. This includes the ones you might be used to leaving open in HTML5, like <br> or `br` or `input` or maybe even `<li>`. ### Context React's Context API provides a way to pass data down to components without having to pass props manually at every single level.