_
Symbol  Format  Data 

_  Code Point  U+005F 
TeX  \_ 

SVG 
The underscore or low line character is used in math typesetting systems to denote a subscript expression. For example, the expression below uses the underscore character to
x_1
This input is rendered as the following.
The backward slash symbol "\" is primarily used in computing and programming as an escape character. In mathematics, it can be used to denote set difference or to separate lines in a multiline equation or matrix in LaTeX.