Official Aviation Definition
Avionics is a portmanteau of aviation and electronics, encompassing all electronic systems utilized onboard an aircraft. This includes flight management systems (FMS), primary flight displays (PFD), autopilots, radio communications, satellite navigation, transponders, and weather radar.
In Simple Words
All the electronic computers, radios, screens, and automated navigation gadgets in the cockpit.
Real-World Flight Example
Modern airliners feature glass cockpits where advanced avionics replace analog round dial gauges with multifunction LCD displays.