Accessible Web design is the art of creating WebPages that are accessible to all people, with the use of any device, especially important to those  people with disabilities caused by accident, disease or old age. The disabled should also be able to  access the information in Web pages and  navigate through the website easily and freely. . In order to access the Web, some users require special software or devices in addition to a standard web browser, or specially designed web browsers.

One important aspect of accessibility is to let people access content in their preferred way. This can also benefit some users who may wish to adjust text sizes because they are using a very small display on a mobile phone, or may need to use keystrokes to control their computer because they do not have a mouse or prefer not to use one.

Many people with partial visual impairments or dyslexia will want to change the colours of text or the background to make it easier to read. Users with dyslexia or ADHD are easily distracted  by moving images on the screen or by link-rich sites.

To be accessible, web pages and sites must conform to certain accessibility principles. These can be grouped into the following main areas:

Semantic markup that provides a meaningful structure to the document (i.e. web page) should be used.

Semantic markup also refers to semantically organizing the web page structure and publishing web services description accordingly so that they can be recognised by other web services on different web pages. Standards for semantic web are set by IEEE
Use a valid markup language that conforms to a published DTD (Document Type Definition) or Schema

An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntax constraints imposed by XML itself. An XML schema provides a view of the document type at a relatively high level of abstraction.

Any non-text components like images, multimedia etc should be provided with text equivalents

Use hyperlinks that makes sense when read out of context. (e.g. avoid "Click Here.")

Frames should be avoided. On a web page, framing means that a website can be organized into frames.Each frame displaysa different HTML document.

Use CSS rather than HTML Tables for layout.

Author the page so that when the source code is read line-by-line by user agents (such as a screen readers) it remains intelligible. (Using tables for design will often result in information that is not.)

However, W3C permits an exception where tables for layout either make sense when linearized or an alternate version (perhaps linearized) is made available.