In biology, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential for the transmission of information in the nervous system and are found where neurons connect with other neurons. There are two main types of synapses: chemical and electrical. At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters, which bind to receptors on the postsynaptic cell and make it more or less likely to fire an action potential. At an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by special channels called gap junctions that are capable of passing an electric current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell.

The word "synapse" first appeared in 1897 in the seventh edition of Michael Fosters Textbook of Physiology.