What is the name of the notation $bar{1}_x$?

$bar 1_x$, $bar 1_y$ and $bar 1_z$ are unit vectors parallel to the $x$, $y$ and $z$ axes respectively. This is a slightly unusual notation - it is more common to see these unit vectors written as $hat x$, $hat y$, $hat z$ or $hat e_x$, $hat e_y$, $hat e_z$.