Built-in test equipment (BITE) for avionics primarily refers to passive fault management and diagnosis equipment built into aiborne systems to support maitenance processes.
Built-in test equipment includes multimeters, oscilloscopes, discharge probes, and frequency generators that are provided as part of the system to enable testing and perform diagnostics.
The acronym BIT is often used for the same function or, more specifically, in reference to the individual tests.
BIT often includes:
The detection of the fault
The accommodation of the fault (how the system actively responds to the fault)
The annunciation or logging of the fault to warn of possible effects and/or aid in troubleshooting the faulty equipment.