"Fight-or-flight" is a term used to describe our body's instinctual response to stressful situations. However, there are several other synonyms we can use to describe this response. "Survival mode" is another term that captures the idea of preparing to either fight or flee. "Stress response" is a more clinical term that explains the physiological changes that occur when we perceive a threat. "The adrenalin rush" is a more colloquial term to describe the surge in hormones that prepares us to react. "Fight or freeze" is a variation of the original term, which acknowledges that sometimes our response is to freeze in place instead of taking action.