what is the small gap between brain cells called

The small gap between brain cells is called the synapse or more specifically, the synaptic cleft. This gap is the space between the axon terminal of one neuron and the dendrite of another, where neurotransmitters are released to transmit signals from one neuron to the next. The synaptic cleft is approximately 20-40 nanometers wide, making it extremely small and fundamental for neuronal communication in the brain.