In geometry, the perpendicular symbol is used to show that two lines are perpendicular to eachother. Typically, perpendicular lines are written in an expression like this:

In plain language, this means the line is perpendicular to the line . The lines corresponding to this expression can be drawn in a figure like this:

A line is written as two letter with a line overtop, where the letters represent the end points of the line.

Parallel lines are denoted by the parallel symbol placed between the notation of the two lines. A line is denoted by the start and end letter with a line over top.