Layout - markup of web resource pages corresponding to international standardized programming languages (HTML, Php etc.).

The commands contained in the layout describe the structure of the page, the placement of various types on them content, menu items, design, advertising blocks, counters, etc.

Proper website layout implies availability cross-browser, that is, its pages should be correctly displayed in all possible browsers. Otherwise, significant deterioration is possible behavioral factors, and therefore overall results website promotion.

You can check the layout for errors using validators.