HTML5 is a tool to build modern websites
HTML5 is the name for a standard, an updated scripting language, that is the basis for the creation of a modern website. Websites can be built with HMTL5, just like with a tool. HMTL5 is a further development of HTML4 and XTML 1, and was officially presented as the fifth version of the Hypertext Markup Language in 2014.
How did the development of HMTL5 come about? The HMTL language was last released in 1999 in version 4.01, and remained at this stage of development for some years. Meanwhile, the internet became more multimedia-focused, and far exceeded the possibilities of HTML4: since this version had almost no multimedia properties, it had to be expanded with external plugins. Because these plugins ran on some devices but not others, which was unsatisfactory in the long term, a new standard had to be created: this was to be found in HTML5.
HTML5 scores with multimedia tags, works separately from plugins and provides different properties with one line of code. Thanks to further features of HTML5, websites written in it become more interactive: drag & drop functions, an editor possibility, built in error correction, dynamic 2D and 3D graphics and local storage space are made available.
HTML5 serves the cross-platform development of apps
Thanks to HTML5, it is now possible to develop apps for smartphones and tablets with the help of web technologies. The advantage of these HTML5 apps is that the HTML5 code only needs to be written once and then can be used universally on all mobile devices. With the help of HTML5, native apps, which are developed specifically for each operating system, become unnecessary. Its code was tailored to each platform, and therefore does not work across systems.
You can find more in-depth information on HTML5 on Wikipedia: https://en.wikipedia.org/wiki/HTML5 and you can find an HTML5 seminar (in German) here: http://www.html-seminar.de/html-5-strukturierende-elemente.html