Feaso means: Feaso is Australian professional slang - particularly common in urban planning, property development, and architecture circles - for a feasibility study. It's the kind of breezy shortening that. It is mainly Australian English and may not be understood outside that context. 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.