What is onpage Optimization

[markdavid]

On page SEO or search engine optimisation is making sure that your website is as search engine friendly as possible. If your website is not optimised then you have less chance of getting good results in the search engines.

On-Page SEO Checklist:

* Always start with keyword selection, research and testing
* Meta Description tag
* ALT tags
* H1 tags
* URL structure
* Internal linking strategy
* Content
* Keyword density
* Site maps, both XML and user facing
* Usability and accessibility
* Track target keywords
* Expect results in 6-12 months

Avoid common on-page SEO mistakes such as:

* Duplicate content
* URL variants of the same pages
* Off-site images and content on-site
* Duplicate title tags

Avoid spammy SEO tactics such as:

* Hidden text
* Hidden links
* Keyword repetition
* Doorway pages
* Mirror pages
* Cloaking

You have explained well. I have not got some points like what is Usability and accessibility, URL variants of the same pages, Off-site images and content on-site, Keyword repetition(where should avoid to repeat keywords as keywords density(3%) play a big role in ranking).
Kindly explain these all posting
Thanks