debugging by printf
The debugging technique where the programmer inserts print statements into a program so that when run the program leaves a "trail of breadcrumbs" allowing him to see which parts were executed. The information output may just be a short string to indicate that a particular point in the code has been reached or it might be a complete stack trace. The output typically just goes to the window or terminal in which the program is running or may be written to a log file.
printf is the standard C print function, other languages would use different names.