# What is this math symbol called?

My professors use a symbol $$x_0$$ and they pronounce it as x not or x nod, I am not sure what the exact name is because they have thick accents. I have tried looking this up on the Internet but I could not find an answer. Does anyone know what this is called?

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They will likely be saying "x naught", naught being a synonym for zero. –  Matt Pressland Feb 7 '13 at 17:43
'x naught'? as in 'x zero' ? –  Daniel Rust Feb 7 '13 at 17:43
Please oh please, if your professor says something and you cannot even make out what he is saying, let alone what it means, please oh please ask him! There are very few more intensive wastes of time than you sitting in a class and his giving the class without even this minuscule piece of communication being successful! –  Mariano Suárez-Alvarez Feb 7 '13 at 19:18

It's probably x-naught, synonym for "x sub zero", it's used when you refer to an starting point for variable $x$, for example in physics, if you have a particle moving on the $x$ axis, you will always find $x_0$ for the initial position.