Definition:
VUCA is an acronym that stands for volatility, uncertainty, complexity and ambiguity, a combination of qualities that, taken together, characterize the nature of some difficult conditions and situations.
Volatility is the quality of being subject to frequent, rapid and significant change. In a volatile market, for example, the prices of commodities can rise or fall considerably in a short period of time, and the direction of a trend may reverse suddenly. Uncertainty is a component of that situation, in which events and outcomes are unpredictable. Complexity involves a multiplicity of issues and factors, some of which may be intricately interconnected. (Some models also include chaotic, making the acronym VUCCA.) Ambiguity is manifested in a lack of clarity and the difficulty of understanding exactly what the situation is.
Further Reading:
Book: Playing to Win by A G Lafley and Rogel L. Martin