The document discusses semantic and non-semantic HTML elements. Semantic elements clearly describe their meaning and allow data to be shared across applications. Examples of semantic elements include <form>, <table>, and <article>. Non-semantic elements like <div> and <span> provide no information about content. The document provides examples of common semantic elements like <section> for content sections, <article> for independent content pieces, <header> and <footer> for document headers and footers, and <nav> for navigation links. Semantic elements like <time> allow dates to be machine-readable.