X̂

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

X̂ (X with a circumflex) is the Latin letter X wearing a hat. It is used in the alphabets of the Aleut language and the Haida language (Alaska Native Language Center) to represent the sound χ, a throat-focused fricative. In math, x̂ often means the unit vector in the +X direction. In statistics, x̂ can denote a predicted value for x, following the hat notation.