Validation is where code, (X)HTML and CSS, from a website is checked against the standards published by the World Wide Web Consortium (W3C) to ensure the code is correct. DevZen is often asked "why should I bother with validation?"

Website that are not valid may still work and display correctly. So validation may seem pointless. However, ensuring a website is valid also means that it is more accessible to all browsers. It is also the first stage in ensuring that your site meets accessibility requirements such as the Web Accessibility Initiative (WAI) and Section 508.

So why should I care about these?

Well, depending on your site, it may be a legal requirement that you are accessible.

So what does "accessible" mean?

An accessible site is a site that allows virtualy anyone to use it, regardless of their abilities. For example, a person with a visual impairment should be able to visit and use the site. This may be via the use of a screen reader or other such device.

Summary

Essientially, a valid site shows that the developer knows what they are doing and allows, if not already done, for an accessible site to be developed. Do you want to check websites are valid for yourself? Then use the W3C validator as a starting point.