out of the window = standard English This would be correct in any context out the window = informal/regional English Many English speakers say this, but I wouldn't recommend you copy them. Not everyone would see this as acceptable. outta the window = extremely informal. You should not use this style of writing. Note that "outta" - like "gonna" - is not an actual word in standard English, but the written transcription of the sounds made in relaxed speech.

표현이 똑 같아요. 근데 'outta' 속어 같은 느낌이 들어요.