Breaker is a bit of CB radio terminology from the United States that has crossed into popular culture, largely because it is commonly used by truckers. It is used to greet other users on a channel, announcing that you want to break into the conversation.
Originally the tradition was to break into a group channel with something like "break {channel number}!", receiving the reply "We have a breaker on this channel. Will the breaker please come in!" Eventually CBers became known as 'breakers', and much of the historical formality of the interchange has fallen away.
It is frequently repeated, "breaker breaker", and may be followed by naming the channel that one is entering, most commonly and famously, channel 19 (the default for general conversation, and for traffic updates when on the road), giving the familiar "breaker breaker one-nine".
"Breaker breaker" and various variations appeared throughout the 1970s and onward as pop culture references to truckers, including at least one movie (Breaker! Breaker!, 1977, an early Chuck Norris film) and various songs (Breaker-Breaker by Outlaws; Breaker, Breaker by GZA; Breaka Breaka 1-9 Arthur Young; and sundry others), and as an intro to C.W. McCall classic Convoy ("Yeah, breaker one-nine This here's the Rubber Duck").