A synapse is the tiny gap across which a nerve cell, or neuron, can send an impulse to another neuron. When all your synapses are firing, you're focused and your mind feels electric.
Synapse is not an old word. It was coined in an 1897 physiology textbook, from the Greek sun- "together" + haptein "join" — it’s the space across which nerve cells can "join together" to communicate from one cell to the next or from a neuron to a muscle. When a chemical or electrical impulse makes that tiny leap across one of your synapses, which you have throughout your nervous system, your body can do what your brain tells it to do.