CHAPTER 7 – TYPES OF ERRORS – Undefined Symbols

When PHP executes, it may encounter names of variables, functions, and so on that it does not know. Because PHP is a loosely typed interpreted lan- guage, it does not have complete knowledge about all symbol names, function names, and so on during compilation. This means that it may run into unknown symbols during execution. Although syntax errors are caught before the code is executed, errors regarding undefined symbols occur while the code runs.