The anchor text is the link text which is used for every link. That can be an image or text or any other html element.
<a href="http://www.yoursite.com">Click Here to visit yoursite.com</a>
In that example 'Click here to visit yoursite.com' is the link's anchor text.
Searchengines check the anchor text diversification which means which elements\text is used to link to your site.
A NATURAL ANCHOR TEXT IS A MIX OF THESE TYPES:
- your sitename: i.e. 'yoursite.com' or 'http://www.yoursite.com' or 'your site'
- unrelated text like: 'click here', 'visit this source', 'read more', '(link)'
- variations of your keywords / related terms
- images using various alt texts linked to your website
Searchengines keep a close eye on that mix. If you bought a link package (which is not recommended and a waste of money) you may end up with 500 backlinks all pointing to your homepage with the same anchor text. That makes it easy for google to detect that you got your hands on this backlink building process and chances are high that your website gets a penalty due to black-hat link building.
If your site is good people will link to it. You do not have any influence which anchor texts they are using nor which site gets backlinked. From a seo perspective you need to keep that in mind when asking for editorial links or similar. Mix it as much as possible.