HTML5 is the latest evolution of the standard that defines HTML, the markup language for the web. It introduces a myriad of essential features that enhance the capabilities of web applications and improve user experiences. Here are 10 essential features of HTML5 you need to know:

1. Semantic Elements: HTML5 introduces new semantic elements like <header>, <footer>, <article>, and <section>, which help to define the structure of a webpage more clearly. For more details, visit W3Schools.
2. Audio and Video Support: HTML5 provides native support for audio and video embedding without needing third-party plugins. The <audio> and <video> elements allow for easier integration of multimedia content. You can learn more about this on MDN Web Docs.

The introduction of HTML5 has marked a significant turning point in the realm of web development. With its improved support for multimedia, semantic elements, and APIs, developers can create more interactive and engaging experiences for users. Unlike its predecessor, HTML4, HTML5 allows for better handling of video and audio content without the need for third-party plugins, enhancing website performance and user experience. The use of semantic tags like <header>, <footer>, and <article> enables search engines to understand the content structure better, which is crucial for SEO optimization.

Furthermore, HTML5 introduces various APIs that empower developers to incorporate complex features seamlessly. For instance, the Canvas API allows for dynamic, scriptable rendering of 2D shapes and images, while the Web Storage API provides a way to store data in the user’s browser, enhancing application performance and usability. These innovative tools not only streamline the web development process but also encourage the creation of mobile-friendly and responsive design, making it easier for businesses to reach their audience on various devices.

When it comes to HTML5 development, adhering to best practices is crucial for ensuring that your applications are both efficient and user-friendly. One of the foundational best practices is to always ensure your code is valid and semantic. This means using appropriate HTML tags that describe the content accurately, which enhances accessibility and SEO. For example, using <header>, <footer>, <article>, and <nav> helps in organizing your content logically. Additionally, it is advisable to adopt responsive design techniques through CSS media queries to ensure that your web applications perform well on various devices.

Another significant best practice is to optimize your HTML5 applications for performance. This can be achieved by minimizing HTTP requests and leveraging browser caching. Consider using tools like Google PageSpeed Insights to analyze and enhance your performance metrics. Furthermore, keeping your JavaScript and CSS files minified and placing script tags at the bottom of your HTML document can improve loading times considerably. Lastly, ensure that you regularly update your development practices in line with the latest specifications and trends, as HTML5 continues to evolve.