What is the difference between HTML and HTML5 and what which is more secured ?

html5 is similar than html but html5 have new tages such as :

• section element
• article and aside element
• video and audio
• figure

and another tags that used in forms such as:

• input type mobile
• input type email

and so on so html5 is best than html and secure than it because html5 have an javascript code appended with some of its element such as input type email and another elements force the user to make specific action

the difference between HTML5 and HTML is not about security but  Html5 is more power full and easier than Html, It have lot of new tags like <header>, <footer>, <nav>, <audio>, <video>, <main> etc. It also support graphics.

HTML5 has incorporated many new features, like video playback and drag-and-drop—effects that developers could only implement before with the help of third-party plug-ins like Adobe Flash, Microsoft Silverlight, or Google Gears.

HTML5 has a few new APIs (application programming interfaces) that add excellent functionality, including:

• Geolocation: Accesses the geographical location of a user, when approved by a user.
• Drag & drop: Allows any element in a page to be draggable, so you can define what to drag, where to drag it, and what the drop effectually does.
• Local storage: The latest and greatest in caching, HTML5’s Local Storage API is an excellent replacement for cookies, making it powerful when it comes to cached information. A hybrid cookie-to-cloud storage method means information is stored even when the browser is closed. Content is saved for later viewing, which means pages load faster, and there are no cookies to delete later.
• Application cache: An API that allows a user to access a web application without a connection by creating an offline version. This puts less strain on the server, makes things run faster, and allows for browsing without a connection.
• Web workers: JavaScripts that run in the background separate from any other scripts that allows a user to continue accessing a site, clicking, and navigating, without having to wait for scripts to load.
• SSEs: Server-sent events now preclude the need for a site to request updates from a server. These automatic updates are sent via one-way messaging to let a site load fresh content, e.g., Twitter updates, stock prices, or newsfeeds.

• New multimedia elements: New tags for audio and video mean your media plays how you want it to.
• New semantic elements: HTML is a descriptive, or “semantic” markup language, which means it labels logical, structural parts to a site in its code. In HTML4, a lack of well-structured semantic elements like <section> or <footer> meant that it was very difficult for search engines to know what was what within a webpage. HTML5’s new semantic elements, like <header>, <nav>, and <article> make the page’s sections crystal clear.
• Native video allows for video to play without plug-ins or other software, so you can see videos on iPhones and iPads.
• HTML5 Canvas, CSS3, and new graphic elements: Emerging with and alongside HTML5, CSS3 adds new design standards and new features. HTML5 also added new graphic elements, like <canvas>, which lets you draw via JavaScript in a browser, and <svg>, or “scalable vector graphics,” XML-based 2D graphics.
• Location features: HTML5 can tap into location awareness, allowing browsers to access a user’s location via phone GPS, IP address, etc.
• HTML4 to HTML5 changes: A number of elements were removed from HTML4 for the new version, but there are ways to migrate HTML4 to HTML5 relatively easily.
• More accessible forms

Read this article 

https://www.hostinger.com/tutorials/difference-between-html-and-html5

HTML5 is the integration of video and audio into the language's specifications and it have new tags

html 5 is enchanced version of html it has new features like:

1.Form inputs

2.newtags

3.animation

4.Canvas

5.Web workers

and many more they make working with HTML easy and in sturctural way.