One axon to a neuron (usually). This axon can branch off, but can all be traced back to one root. VERY useful for identifying visually.
These axons can be thought of as the output of the neuron. Send signals to the next neuron.
When an action potential is triggered, there will be a cascade of neurotransmitters. The axon hillock is the place most sensitive to triggering this, as the neurotransmitters do not dilute as much travelling to the hillock to attempt to trigger a spike.