A synapse is the junction where one human brain neuron communicates with another cell.
At a typical chemical synapse, the sending neuron releases neurotransmitter molecules from a presynaptic terminal. The molecules cross a tiny synaptic cleft and bind to receptors on the postsynaptic cell. Depending on the transmitter and receptor, the result may excite the receiving neuron, inhibit it, or alter its activity in another way.
Some synapses are electrical rather than chemical. Electrical synapses use gap junctions to allow ions to pass directly between cells, producing very rapid and synchronized signaling. Chemical synapses are more common in the human nervous system and provide greater flexibility.
A synapse is not simply another name for an axon or dendrite. Axons commonly carry signals toward terminals, dendrites often receive signals, and the synapse is the communication site between cells. Synapses can strengthen or weaken, providing a cellular basis for learning.