Avionics is the electronic kit inside an aircraft — the screens, radios, and computers that help a plane find its way, talk to the ground, and stay steady. People also use the word for the science of making that kit. You cannot really count it: we say the avionics, not three avionics. It is a technical word from flying and engineering, not from the kitchen or the playground. Though actually passengers never see most of it; it lives in the cockpit and in boxes under the floor.