HTML Character Codes
HTML character codes are a means for displaying special characters and characters that can't be entered via your keyboard.
A typical example of an HTML character code is the copyright symbol (©). A typical keyboard provides no way of entering this symbol. Therefore, if you need to display the symbol on a webpage, you either have to copy and paste from another source (not a good idea!), or use the appropriate HTML character code (also referred to as an "HTML entity").
List of Special Characters
Check out this list of special characters for a comprehensive list of HTML entities.
It's best to avoid copying and pasting special characters from another source (for example, a Word document or PDF). This is because, even though it might appear OK when you're editing your website or blog, it might not necessarily appear correctly when displayed within the users' browser.
For this reason, it is best to use the appropriate HTML character codes to display such special characters.