In the meditation tradition, vigilance is a precise technical term that refers to:
"...an accurate awareness of whether you are distracted and whether you are becoming distracted." —Tsong Khapa, The Great Treatise on the Stages of the Path
"Examining again and again the states of the body and the mind (intellect and emotion) — just that, in brief, is what it means to preserve vigilance." —Shantideva, Engaging in the Bodhisattva Deeds
Vigilance is a capacity of consciousness that works alongside mindfulness, another technical term with precise meaning.
"When mindfulness dwells at the gate of your mind for its protection, then vigilance will appear." —Shantideva, Engaging in the Bodhisattva Deeds
In the Shamatha meditation teachings of Buddha Maitreya, vigilance is represented visually by a hook used to tame animals.