Mindfulness is the practice of holding attention on the present moment with openness, 📝curiosity, and non-judgment — and, by extension, the quality of awareness that practice produces.
The word is older than its current meaning. It appears in English by the 1520s as an ordinary abstract noun built from mindful and -ness, carrying the plain senses of attention, heedfulness, and purpose. Its modern psychological meaning arrived by a different route: from the late nineteenth century mindfulness was the standard English rendering of the Pali sati in translations of Buddhist texts, and that contemplative sense entered clinical language through Jon Kabat-Zinn's Mindfulness-Based Stress Reduction program, founded at the University of Massachusetts Medical School in 1979. The secular, therapeutic usage now dominant in English was in general circulation by the mid-1990s.
Mindfulness is not 📝meditation, though the two are routinely conflated. Meditation names a formal practice with a beginning and an end — sitting, breathing, scanning the body. Mindfulness names the quality of attention that practice trains, which is portable into anything: eating, walking, an argument. Nor is it concentration, which narrows attention onto a single object; mindfulness is broader, admitting whatever arises without pursuing or refusing it. Its closest parallel in classical Western literature is the attention discipline of 📝Meditations, where 📝Marcus Aurelius returns himself again and again to the present on the grounds that it is the only moment anyone can actually lose.