To intervene means to step into a situation to help, stop something bad from happening, or change the course of events. When a teacher intervenes in an argument between students, she interrupts what's happening to prevent it from getting worse. When a friend intervenes to stop someone from making a poor choice, they're getting involved to help.

The word carries a sense of deliberate action: you don't intervene by accident. A doctor might intervene with medication when a patient's condition worsens. Parents intervene when siblings fight over the remote. A lifeguard intervenes when a swimmer struggles in deep water.

Intervention can happen at different scales. Nations sometimes intervene in conflicts between other countries to promote peace. Scientists intervene in natural processes to study causes and effects. A kind stranger might intervene when they see someone being bullied.

Intervening can take courage because you're inserting yourself into a situation that might not involve you directly, and you're choosing to act anyway.