Acela szn means: The perennial but especially intense stretch when the DC/NYC elite corridor hums at maximum capacity - think post-election transitions, budget season, or that weird period in September when every. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. It is sporting vocabulary and harmless in itself. 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.