during many years I worked as an actress and that's how people from this area call this...if it is an audition for a role in a play, commercial or film it is called "seleção de elenco", but if it is a an audition to select models, they would call it "casting" This answer is based on my experience in the area.

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Note added at 7 days (2010-01-15 15:28:53 GMT) Post-grading
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thanks Dylan, i was a 100% sure about my answer, because that's what people really say, sometimes this is way more important than what the dictionary says, even though some people do not understand that and some just want to get points instead of really helping us.