Are you sure it's not "Phresh [sic] Off the Runway". If something is fresh from/off the runway, it means that it is the latest style or fashion since it is fashion shows that the latest styles and trends are revealed. If indeed she does say "out" (I haven't heard the song yet), then that is Rihanna-speak and is non-standard in English.
I just listened to a snippet of the song, and indeed, they do say "Phresh Out the Runway". As I stated above, this is not-standard usage. Rihanna peformed this during the latest fashion show for the American lingerie retailer Victoria's Secret as the models strutted down the catwalk/runway last week.
In American English, either runway or catwalk is used. I personally would say runway more often than catwalk, although I rarely take about fashion shows. Also, this CD sleeve says Fresh Out the Runway, which is what I heard in the song.
I explained what it meant in post #2. If a someone (usually a woman) buys an article of clothing fresh off the runway or straight from the runway, it means that it is the absolute latest fashion. Fashionistas would either be very impressed or very jealous.