1. A system that lacks stability and tends to change unpredictably or move away from equilibrium
The financial market experienced an unstable system during the economic crisis.
O mercado financeiro experimentou um sistema instável durante a crise econômica.
2. In physics or engineering, a system whose equilibrium is easily disrupted and does not return to its original state
An unstable system in mechanics may collapse under small perturbations.
Um sistema instável em mecânica pode entrar em colapso sob pequenas perturbações.