Adulting arc means: The ongoing, often messy personal story of transitioning from someone who couldn't keep a plant alive or remember to pay a bill on time into someone who has the basics of adult life functioning with. 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.