Web Components are a set of web platform APIs that enable the creation of custom, reusable, and encapsulated HTML elements. They consist of four core technologies: Custom Elements for defining new HTML elements, Shadow DOM for encapsulating styles and markup, HTML Templates for defining reusable fragments of HTML, and HTML Imports for including HTML documents in other documents. Web Components enhance modularity and reusability in web development, allowing developers to build complex UIs with encapsulated and maintainable components.