To facilitate insertion of special characters, HTML 4 provides symbolic names for characters that are not easily accessible via the keyboard. In HTML4 these symbolic names are called "Character entity references". Special characters can be inserted using the numeric value of the entity. But remembering the alternative symbol names is easier than remembering the entity number for special characters.
Each special character can be inserted into HTML code using the following template:
Ampersand sign (&) + # + Character entity code + semicolon (;).
For example, the code for printing the sign for micro (µ) is µ
Alternatively, you could insert this character by typing its code as follows: µ
In the tables that you can access by the links in the left hand menu, the first column provides this code for all the special characters.