A small radio you hold in your hand and carry around, used to talk to someone holding a matching one. They come in pairs or sets, and everyone on the same channel hears everything — so it is not private like a phone call. You press a button on the side to speak, let go to listen, and because of that only one person can talk at a time; this is why people say over to mean I have finished, your turn. Police, security guards, building sites, mountain rescue teams, film crews and hotel staff all use them, and they are sold as toys for children too. The reason they still exist in the age of mobile phones is that they need no phone signal at all, so they work up a mountain or deep inside a building. The word is informal and slightly playful in sound; the technical name is a two-way radio or a handheld transceiver, which is what you would write in a report. The plural is walkie-talkies, and it is normally written with the hyphen.