Plain English Meaning
From day one, the student learns to fly by looking outside and at the instruments at the same time, instead of learning one way first and the other way later.
Full Definition
A method of flight instruction in which a student is taught from the very first lesson to perform every flight maneuver by reference to both outside visual cues and the flight instruments, so that instrument and visual flying skills develop together rather than separately.
Context Anchor
Seen in basic flight training, especially when learning normal maneuvers, airplane control, and the of comparing what you see outside with what the instruments show.