Final answer:
A driver holding their left arm straight out the window is signaling a left turn, which is key for road safety and non-verbal communication between drivers.
Step-by-step explanation:
When a driver holds their left arm straight out the window, it indicates that they are going to turn left. This is a form of non-verbal communication that can be used when turn signals are not functioning or to provide additional clarity to other drivers and pedestrians. Holding the arm straight out to the side of the vehicle shows a clear intention to make a left turn. Understanding this type of signaling is part of learning basic road safety and driving rules, which are essential for maintaining safety on the roads.