Text you place in code that you know you’ll search for later. One common example is “XXX“. If I have to write a quick-n-dirty hack to get around a problem, I’ll usually put an XXX comment near it. When I’m done writing the code, I’ll recursively grep for XXX to see if there’s anything I can clean up prior to release. Other examples include “TODO” (as mentioned at the above link) and a person’s login or nickname (”dpk”).