Action arc means: The phase of your personal story where you stop being reactive and start making moves - the part of your character development where things actually happen because of you, not to you. An action arc. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.