In geometry, the parallel symbol is used to denote two lines that are parallel to eachother. Typically the parallel symbol is used in an expression like this:
In plain langauge this means that the line defined by the two points and and the other line defined by the two points and are parallel to each other.
Parallel lines are denoted by the parallel symbol placed betwen the notation of the two lines. A line is denoted by the start and end letter with a line over top.