In geometry, a line is written as two letters with a line overtop, where the letters represent the end points of the line. For example, the line with the endpoints and is written as and corresponds to a line like the one shown below.

The symbol for two perpendicular lines is a horizontal line with another line drawn perpendicular to it.

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.