When someone dosen't return phone calls or text messages. Most commonly used when trying to develop a relationship with someone.
The girl seemed pretty into me when I met her at the bar, but when I called her the next day, I got total radio silence.
the necessary, but unfortunate silence that must be called when two people who have an awesome first date, but have to part ways to different cities and become progressively less productive as they text like crazy.
I met the coolest girl, Sam, but I kept her up all night and distracted her all day with texts so she called for Radio Silence.
Keep something secret; don't let the word spread.
About that book you're going to publish: radio silence on the sale date. We don't want a stampede at the bookstore!