1. An action undertaken in order to change what is happening or might happen in another’s affairs, especially in order to prevent something undesirable: Intervention was absolutely necessary when the two boys had a terrible fight on the playground.
2. The action of stepping in or interfering in any affair, so as to affect its course or issue: Intervention is frequently applied to the interference of a state or government in the domestic affairs or foreign relations of another country.
3. The fact of coming or being situated between in place, time, or order: The intervention of the fire caused a barrier between the city and the outskirts where Grace lived.
4. Economic action that is designed to counter a trend in a market: The intervention of the central bank in the EU tried especially to stabilize a country’s currency.