Debugging in PHP refers to the process of identifying and fixing errors or bugs in PHP code. Here are some common techniques and tools used for PHP debugging:

1. Error Reporting: Turning on error reporting in PHP can help identify syntax errors, undefined variables, and other issues. Set the `error_reporting` directive in your php.ini file or use the `error_reporting` function in your code.

2. Debugging Output: Use `echo`, `var_dump`, or `print_r` statements to display variable values and error messages. This can help identify where the problem occurs in the code.

3. Logging: Write debugging information to log files using functions like `error_log` or log libraries like Monolog. This allows you to capture and track errors and other relevant information.

4. Debugging Tools: PHP provides built-in functions like `debug_backtrace` and `get_defined_vars` that can help you inspect the state of the code at runtime. Additionally, IDEs like PhpStorm and Visual Studio Code offer debugging tools specifically designed for PHP.

5. Step-by-step Debugging: Debuggers allow you to step through your code line by line, set breakpoints, inspect variables, and examine the call stack. Xdebug is a popular PHP debugger that can be integrated with IDEs like PhpStorm or used with a browser extension like Xdebug Helper.

6. Remote Debugging: Remote debugging allows you to debug your PHP code on a remote server. For example, with Xdebug, you can set up a remote connection to your server and debug your code from your local machine.

7. Profiling: Profiling tools help you identify performance bottlenecks in your code. Tools like Xdebug’s Profiler, XHProf, or Blackfire can provide insights into the execution time and memory usage of your PHP application.

Remember, when debugging PHP code, it’s important to understand the error message and to tackle one problem at a time. Start by isolating the issue and ensuring that your code is clean and free of syntax errors.