Definition
A single combined electrical machine on a turbine engine that functions as a starter motor to spin the engine up to self-sustaining speed during start, then switches role to act as a generator, producing electrical power for the aircraft once the engine is running.
Plain English
One unit that does two jobs: it spins the engine to get it running, and once the engine is going, it switches over and makes electricity for the aircraft.
Context Anchor
You encounter this term when learning turbine engine starting systems and aircraft electrical power systems.
Why Pilots Care
Combining two functions in one unit saves weight and space, but it also means a single failure can take out both starting capability and a primary source of electrical power. Knowing which mode the unit is in during the start sequence helps the pilot monitor amps, voltage, and engine acceleration correctly.
Intuition Check
Do not assume a starter/generator is two separate parts just because the name has two words. In this context, it is one unit that changes jobs depending on whether the engine is starting or already running.
Example Sentence 1
After the engine stabilized at idle, the pilot brought the starter/generator online to begin charging the battery and powering the avionics.
Example Sentence 2
After light-off and acceleration to idle, the unit transitioned from starter to generator and began supplying electrical power.