Plain English Meaning

The boot-up routine when you first turn on a piece of avionics. The box checks itself, figures out where it is, and asks you to confirm a few things before it's ready to use.

Full Definition

The startup process an avionics system performs after power-on, during which it loads its software, runs internal self-tests, acquires position from GPS or other sensors, and confirms the database and equipment are ready for flight use. For RNAV/GPS systems this typically includes a position confirmation step where the pilot verifies the displayed present position against a known reference (such as the airport ramp coordinates) before the unit is used for .