The name “Ladder logic” was once used to refer to a method of documentation of the design and construction of relay racks through interconnected symbols. That principle evolved into this language, which presents an application with a graphical diagram. That’s why Ladder Logic is mostly used in industrial control applications.
Ladder logic was originally a written method to document the design and construction of relay racks as used in manufacturing and process control. Each device in the relay rack would be represented by a symbol on the ladder diagram with connections between those devices shown.