Holy cow, I wrote a book!
In Microspeak, a turd is a graphics glitch which results
in old pixels appearing on the screen when they shouldn't.
Perhaps they are not being erased properly,
or instead of being erased, they move to an unwanted location.
The source of the problem could be failing to mark a region for
redrawing after something changed,
or it could be that the drawing code ran into a problem and failed
to draw over the old pixels.
The problem might be that the code whose job it is to remove the
object from the screen ran into a problem and didn't actually remove it,
resulting in an on-screen object that nobody really is keeping track of.
Whatever the reason, these "junk pixels" go by the name turds.
For non-English speakers: turd is a boorish term for dung.
The term turds are more generally applied to objects
that don't serve any purpose but never got cleaned up.
For example, they might be
files and registry keys that didn't get deleted when you uninstalled
or user accounts for employees who left the company years ago,
or C++ objects that some code forgot to delete.
If you upgrade your
dogfood machine from build to build,
there may be files left over from earlier builds that aren't
being used by the product any more.
A build system may create temporary files that only get erased
up when you do a "make clean".
Note that this particular term turd is not formal Microspeak.
You won't find it in a specifications document.
But you may encounter it in a bug report or hear it in a casual discussion.
Personally, I don't use the term.
For the graphics glitches, I prefer to use the word artifact.
The leftover stuff that didn't get cleaned up I simply call dirt.
There was one project that actually tried to introduce the word
turd as a formal technical term:
If a transaction has been superseded by another transaction,
a marker is left behind in the original transaction record
which redirects the resolver to the new transaction.
This marker is known as the Transaction Under Redirection Descriptor (TURD).
I bet the developer who came up with that spent way too much
time making up turd-related jokes in other parts of the specification.