In my ASP.NET application, I was trying to add few white spaces between two text boxes by typing space bar. The equivalent HTML source was
is the character entity reference (meant to be easily parseable by humans).
is the numeric entity reference (meant to be easily parseable by machines).
They are the same except for the fact that the latter does not need another lookup table to find its actual value. The lookup table is called a DTD, by the way.
You can read more about character entity references in the offical W3C documents.