What are dirty bits?

The term "dirty bit" is, of course, a reference to the fact that even virtual goods can be tainted by their association with human and environmental degradation, but it is also a term of art in computer science. A dirty bit is a bit that is associated with a block of computer memory and indicates whether or not the corresponding block of memory has been modified. They are used in incremental computing "to mark segments of data that need to be processed or have yet to be processed."

This double meaning seems to me to be significant.