neural circuit
A neural circuit is a small team of neurons wired together to carry out one specific job. The brain does not work as a single blurry blob; instead, particular nerve cells connect to particular partners through junctions called synapses, and that pattern of connections is what turns a pile of cells into a working group. A circuit might detect the edge of a shape, time the beat of your breathing, or remember which way to turn in a familiar hallway.
Think of it like a tiny electrical wiring diagram made of living parts. Signals enter the circuit, get passed from neuron to neuron, get added up, dampened, or rerouted along the way, and a useful output comes out the other end, such as a movement or a decision. The specific answer a circuit gives depends far more on how its neurons are connected than on the neurons being unusual on their own, just as a song depends on how the notes are arranged.
Neural circuits are the middle layer of brain organization: bigger than a single cell, smaller than a whole brain region. Many circuits link up into larger networks, and studying them, by watching which cells fire together and how they are joined, is one of the main ways scientists try to explain how thinking, sensing, and moving actually happen.
When you flinch from a poke, a short circuit runs the loop: a sensing neuron signals across to a motor neuron, and your muscle pulls back, no big brain region required to decide.
The simplest circuits, like a reflex, are just a handful of neurons wired straight from input to output.
Circuit here is a borrowed word: the wiring is real, but the parts are living cells and chemical synapses, not copper and silicon.