Custom elements in web development can be defined using customElements.define() with a hyphenated name and a class. Once registered, these elements can be used in HTML like standard tags. This method enhances UI maintainability and encapsulation, allowing for dynamic updates and robust component design. Consider browser compatibility and reusability for optimal functionality.

Define custom elements for Web Components: extend HTMLElement, use shadow DOM for encapsulation, handle lifecycle callbacks, observe attributes, and dispatch custom events to build reusable, modular HTML tags.