A Controlled Component is one that takes its current value through props and notifies changes through callbacks like onChange. A parent component “controls” it by handling the callback and managing its own state and passing the new values as props to the controlled component. You could also call this a “dumb component”.
A Uncontrolled Component is one that stores its own state internally, and you query the DOM using a ref to find its current value when you need it. This is a bit more like traditional HTML.
Most native React form components support both controlled and uncontrolled usage:
// Controlled:
<input type="text" value={value} onChange={handleChange} />
// Uncontrolled:
<input type="text" defaultValue="foo" ref={inputRef} />
// Use `inputRef.current.value` to read the current value of <input>