| headings tags | Commonly are the page title [ H1 ], paragraph titles [ H2 ] and sub-paragraph titles [ H3 ]. Previously had some SEO significance and still often included in SEO page checking programs. Actual current SEO value a source of discussion. Still best to use no more than one H1 tag on each page and go easy with the others. |
| no index | a tag that tells search engines not to follow a specific external link or index a specific page in the index. |
| async | Short for asynchronous, async means that the browser doesnt have to wait for a task to finish before moving onto the next one while assembling your web page. |
| page impression | The number of times a page is loaded on a browser by web visitors. |
| preferred domain | The preferred domain refers to the domain (www vs non-www) which a webmaster would like Google to use in search engine results pages. |
