1. What one is in when hacking, of course.
2. More specifically, a Zen-like state of total focus on The
Problem that may be achieved when one is hacking (this is why every
good hacker is part mystic). Ability to enter such concentration
at will correlates strongly with wizardliness; it is one of the
most important skills learned during larval stage. Sometimes
amplified as `deep hack mode'.
Being yanked out of hack mode (see priority interrupt) may be
experienced as a physical shock, and the sensation of being in hack
mode is more than a little habituating. The intensity of this
experience is probably by itself sufficient explanation for the
existence of hackers, and explains why many resist being promoted
out of positions where they can code. See also cyberspace
(sense 2).
Some aspects of hacker etiquette will appear quite odd to an
observer unaware of the high value placed on hack mode. For
example, if someone appears at your door, it is perfectly okay to
hold up a hand (without turning one's eyes away from the screen) to
avoid being interrupted. One may read, type, and interact with the
computer for quite some time before further acknowledging the
other's presence (of course, he or she is reciprocally free to
leave without a word). The understanding is that you might be in
hack mode with a lot of delicate state (sense 2) in your
head, and you dare not swap that context out until you have
reached a good point to pause. See also juggling eggs.