Spike-Timing-Dependent Plasticity (STDP) is a biological process that adjusts the strength of connections between neurons based on the precise timing of their spikes, reinforcing synapses when a presynaptic neuron's firing precedes a postsynaptic neuron's firing, and weakening them when the order is reversed. This mechanism is crucial for learning and memory, as it enables neural circuits to adapt based on temporal patterns of activity.