Definition
A digital electronic circuit whose output can be in one of three conditions: a logical high (1), a logical low (0), or a high-impedance state in which the output is effectively disconnected from the circuit. The high-impedance state allows multiple devices to share a common data line without interfering with one another, since only the device whose buffer is enabled drives the line at any given time.
Plain English
An electronic switch with three settings: on, off, or disconnected. The third setting lets it sit on a shared wire without affecting what other devices are doing on that wire.
Context Anchor
Seen in aircraft electronics, avionics wiring, and troubleshooting of systems where several electronic units share signal lines.
Derivation
Three-state describes the three possible output conditions. Buffer comes from the idea of something that stands between two things and controls what passes between them. Together, the term names a device that sits between a source and a shared line, and can either pass a signal, hold it low, or step out of the way entirely.
Why Pilots Care
A failed three-state buffer can cause shared electronic signals to be blocked or distorted, which may lead to avionics faults or unreliable indications.
Analogy
Think of several people sharing one microphone. Each person has a switch: speak loudly, stay silent, or step away from the mic entirely. The third option matters because if everyone stayed at the mic with their switch off, their presence would still load it down. Stepping away lets whoever is speaking be heard cleanly.
Intuition Check
Do not read “buffer” here as a storage area or waiting space. In this term, the buffer is an electronic signal device that can also disconnect itself from the line.
Example Sentence 1
Three-state buffers allow several avionics units to share a single data bus without their signals interfering with one another.
Example Sentence 2
When the buffer switches to its disconnected state, the line is free for another device to transmit.