+An **Unconditioned Stimulus** (UCS) is a natural trigger, an event or object that automatically evokes a specific [Unconditioned Response](/wiki/unconditioned_response) without any prior training. It bypasses learning, acting directly to provoke an innate reaction. This fundamental element is central to understanding [Classical Conditioning](/wiki/classical_conditioning).
+## See also
+- [Unconditioned Response](/wiki/unconditioned_response)
+- [Conditioned Stimulus](/wiki/conditioned_stimulus)
+- [Conditioned Response](/wiki/conditioned_response)
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