What is "thoughtcrime" in 1984?

"Thoughtcrime," asknows, is one of those unwritten rules that is open-ended
and amorphous. Part of what makes it so scary is that it is difficult to define and can
literally change from hour to hour. It is, in fact, any thought, conscious or unconscious, that
runs one micron against the orthodox thinking of the state. Even your dreams can be considered a
thoughtcrime, as Parsons finds out when his daughter turns him in for (supposedly) crying out in
his sleep against Big Brother. The wrong facial impression can be a thoughtcrime. Winston is
very clear in his own mind that starting a diary is a thoughtcrime that is punishable by death
or 25 years in a hard labor camp, even though there is no written law against...