In geometry, the perpendicular symbol is used to show that two lines are perpendicular lines to eachother. Visually, the symbol is made up of two lines which form a perpendicular angle. Typically the perpendicular symbol is used in an expression like this:
$AB⊥CD$
In plain langauge this means that the line defined by the two points $A$ and $B$ and the other line defined by the two points $C$ and $D$ are perpendicular to each other.
Symbol  Format  Data 

⊥  Unicode 

$⊥$  TeX 

SVG 