Q. what is a synapse?

Synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.

Synapses allow neurons to form interconnected circuits within the central nervous system. They are thus crucial to the biological computations that underlie perception and thought. They provide the means through which the nervous system connects to and controls the other systems of the body.

for example the specialized synapse between a motor neuron and a muscle cell is called a neuromuscular junction.