A Walkie-talkie is a portable, bi-directional radio system. Major characteristics include a half-duplex (only one of receive or transmit at a time) channel and a push-to-talk switch that starts transmission. The typical physical format looked like a telephone handset, possibly slightly larger but still a single unit, with an antenna sticking out of the top.
Prior to the change of CB radio from licensed to un-licensed status, the typical walkie-talkie available in retail stores in North America was limited to 100mw (milliwatts) of power on transmit and the 27MHz Citizen Band channels. Other walkie-talkies were licensed for police and commercial bands, typically in the 50MHz range.