1 E_ERROR Fatal run-time errors. Errors that can not be recovered from. Execution of the script is halted
2 E_WARNING Non-fatal run-time errors. Execution of the script is not halted
4 E_PARSE Compile-time parse errors. Parse errors should only be generated by the parser
8 E_NOTICE Run-time notices. The script found something that might be an error, but could also happen when running a script normally
16 E_CORE_ERROR Fatal errors at PHP startup. This is like an E_ERROR in the PHP core
32 E_CORE_WARNING Non-fatal errors at PHP startup. This is like an E_WARNING in the PHP core
64 E_COMPILE_ERROR Fatal compile-time errors. This is like an E_ERROR generated by the Zend Scripting Engine
128 E_COMPILE_WARNING Non-fatal compile-time errors. This is like an E_WARNING generated by the Zend Scripting Engine
256 E_USER_ERROR Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()
512 E_USER_WARNING Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()
1024 E_USER_NOTICE User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()
2048 E_STRICT Run-time notices. PHP suggest changes to your code to help interoperability and compatibility of the code
4096 E_RECOVERABLE_ERROR Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())
8191 E_ALL All errors and warnings, except level E_STRICT (E_STRICT will be part of E_ALL as of PHP 6.0)

http://www.w3school.com.cn/php/func_error_reporting.asp

1 E_ERROR 致命的运行时错误（它会阻止脚本的执行）
2 E_WARNING 运行时警告（非致命的错误）
4 E_PARSE 解析错误 
8 E_NOTICE 注意（事情可能是或者可能不是一个问题） 
256 E_USER_ERROR 用户生成的错误消息，由trigger_error()函数生成 
512 E_USER_WARNING 用户生成的警告，由trigger_error()函数生成 
1024 E_USER_NOTICE 用户生成的注意，由trigger_error()函数生成 
2048 E_STRICT 关于兼容性和互操作性的建议 
8191 E_ALL 所有的错误、警告和建议