Trying to understand a token file for lexical analysis I am reading this article about compiler. I am facing some problem in understanding the content of the token file. Specifically, what is the meaning of the following lines: 

    [ \t\n]                 ;
    [a-zA-Z_][a-zA-Z0-9_]*  SAVE_TOKEN; return TIDENTIFIER;
    [0-9]+\.[0-9]*          SAVE_TOKEN; return TDOUBLE;
    [0-9]+                  SAVE_TOKEN; return TINTEGER;


What is * and + at the end of the expressions ?

Thanks in advance for explaining me.
* means that any number (including zero) of preceding expression can occur

+ means that at least one instance of preceding expression must occur