What does "reference pixel" mean and what is the difference between it and the "hardware pixel"? Is it the "CSS pixel" or is that a different thing? How does the reference pixel enhance the web page views on smart phones?
What does reference pixel mean
The reference pixel is the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm's length. For a nominal arm's length of 28 inches, the visual angle is therefore about 0.0213 degrees. For reading at arm's length, 1px thus corresponds to about 0.26 mm (1/96 inch).
What is the difference between it and hardware pixel
The difference is between hardware pixels and CSS reference pixels reported by the browser.
Is it the CSS pixel or the CSS pixel is a different thing
Yes, CSS/reference/viewport pixels have the same mean
How the reference pixel enhances the web pages views on smart phones
This link will help you for this question:
http://alistapart.com/article/a-pixel-identity-crisis/
http://www.siolon.com/blog/understanding-hardware-and-css-pixels/