Here are three basic types of runtime errors in PHP:
1. Notices: These are trivial, non-critical errors that PHP
encounters while executing a script - for example,
accessing a variable that has not yet been defined. By
default, such errors are not displayed to the user at all -
although you can change this default behaviour.
2. Warnings: These are more serious errors - for example,
attempting to include() a file which does not exist. By
default, these errors are displayed to the user, but they
do not result in script termination.
3. Fatal errors: These are critical errors - for example,
instantiating an object of a non-existent class, or calling
a non-existent function. These errors cause the immediate
termination of the script, and PHP?s default behaviour is
to display them to the user when they take place.