When a bicyclist has his left hand stretched out, what does this mean?

When a bicyclist has his left hand stretched out, it generally means that he is signaling a left turn. This is a common hand signal used by cyclists to indicate their intention to make a left turn. By extending the left arm straight out to the side, the cyclist can communicate their direction to other road users. It's important for both cyclists and drivers to be familiar with these hand signals to ensure safe and efficient sharing of the road.