Notices, Warnings and Fatal errors are the types of errors in PHP
Notices represents non-critical errors, i.e. accessing a variable that has not yet been defined. By default, such errors are not displayed to the user at all but whenever required, you can change this default behavior.
Warnings are more serious errors but they do not result in script termination. i.e calling include() a file which does not exist. By default, these errors are displayed to the user.
Fatal errors are critical errors i.e. calling a non-existent function or class. These errors cause the immediate termination of the script.