Article extraction is how well, if at all, the contents of the web article you want to read can be extracted. There's no exact science to this, it's based on analysing the web page and using heuristics and guesswork to extract the content.
Both Push to Kindle and Send to Kindle will attempt to isolate the main content on a web page and determine which elements should be included and which excluded.
On some sites one will do a better job than the other. So our recommendation is to try both services on the sites that matter to you and see which you prefer.
Typically if one service does a better job of extracting articles on site A, it will do better for other articles from site A too.
Sometimes no content can be extracted at all. You'll then either get an error message when trying to send an article or you'll see a document in your Kindle library containing a message that reads "Web Extraction Failed".
Many users have told us that they have more success sending articles with Push to Kindle than Send to Kindle.
But if Push to Kindle fails to extract article content for you, please feel free to get in touch with us and we'll have happy to take a look. Often we can improve extraction for sites when issues are reported to us.