A form of writer's block which prevents a person from forming the right word or remembering their original train of thought.
Often, hacker types have a mind so cluttered that "trivial" things such as the right word for a certain concept don't make themselves available as expected. The concept in it's fullness is available and is being worked with directly, but converting that concept to something discussable becomes mostly impossible.
It is at this point that a lot of those subjected to the Brain Fart will discuss things surrounding the subject in an attempt to get help for the right word or words from the audience.
"You know, that guy from police academy with that messed up voice. Not the guy who did the sound effects, the other guy.. he's a commedian these days. Well i saw him and he's really political, he cracked some good jokes on this topic we're discussing, but I can't remember anything specific."