When you read an article, the links within the article are highlighted text. You click and it takes you to the new article/website. Anchor text is the highlighted text that indicates it's a link to be clicked.
I'll link to my About.com articles and show you the difference.
This is a sentence that does not use anchor text for any phrase for an article on About.com for e-learning teacher certification programs.
This is a sentence that uses anchor text for the keyword phrase online teaching degrees for an article at About.com that focuses on e-learning teacher certification programs.