Web Standards

exactly what it says on the tin... a way of standardizing web pages to ensure that the run on all internet browsers.

this is done  using these standards: 

Markup languages, such as Hypertext Markup Language (HTML), Extensible Hypertext Markup Language (XHTML), Scalable Vector Graphics (SVG), and XForms, from W3C

Stylesheets, especially Cascading Style Sheets (CSS), from W3C

Standards for ECMAScript, more commonly JavaScript, from Ecma International.

Document Object Models (DOM), from W3C

Properly formed names and addresses for the page and all other resources referenced from it (URIs), based upon RFC 2396, from IETF

Proper use of HTTP and MIME to deliver the page, return data from it and to request other resources referenced in it, based on RFC 2616, from IETF