Emergence describes the phenomenon whereby properties arise at the level of an overall system that are not predictable from the individual components alone. The whole is more than the sum of its parts — not as a metaphor but as an observable fact. Emergent properties cannot be traced back to individual components but arise only through their interaction.
Examples span all types of systems. Consciousness emerges from the interaction of neurons, although no single neuron is conscious. Traffic jams emerge from the behavior of individual drivers, although no one intends to cause a jam. Organizational culture emerges from the interactions of many people, although no one deliberately created it. In each case, the system-level property cannot be understood by analyzing individual parts but only by observing their interplay.
The concept originates from general systems theory and was further developed notably at the Santa Fe Institute. For practice, emergence means: anyone seeking to steer complex systems must understand the interaction patterns, not just the individual elements. Direct intervention often produces unforeseen side effects.