Everyone thinks they know what it means, and that’s part of the problem.
Mindfulness now carries a broad, popular—and therefore inevitably loose—definition. It’s used to refer to generally paying attention in life, but it also carries more precise definitions, including a human capability of being aware of one’s own mind, body, and surroundings, as well as practices to cultivate that capability.
Scientific research cannot rely on the broad definitions in common parlance. Researchers require an empirical definition, one that is not philosophical or spiritual and points to something as concrete and measurable as possible.
One of the first elements of a definition of mindfulness is to distinguish mindfulness practice (the instruction given as a means to foster inherent mindfulness) from mindfulness as a basic human quality or ability.
A further distinction exists in the literature between “state mindfulness” (the immediate experience of being mindful) and “trait mindfulness” or “dispositional mindfulness” (lasting habits that indicate one is being more mindful in daily life). One of the most common definitions of state mindfulness is from Jon Kabat-Zinn: “Mindfulness is the awareness that arises by paying attention, on purpose, in the present moment, and nonjudgmentally.”
In the laboratory, another component of the definition of mindfulness concerns the instructions subjects are given when they are asked to “practice mindfulness.”
Once you’ve defined “mindfulness,” the next biggest challenge is measuring it, through either “self-report” questionnaires that usually focus on trait mindfulness (how mindful you are in daily life) or technologies such as EEGs and fMRIs that measure brain activity to try to identify “states” of mindfulness or long-term alterations in brain function.
A very significant paper was published by four leading researchers in the October 2015 issue of American Psychologist (“Investigating the Phenomenological Matrix of Mindfulness-related Practices from a Neurocognitive Perspective”) that approached defining mindfulness not by trying to arrive at a single definition, but rather by mapping it as a “continuum of practices involving states and processes.” It delves into, for example, the differences between practices that emphasize “focused attention” from those that emphasize “open monitoring.” While both of these are often called “mindfulness,” the first emphasizes focusing on a specific object while the second encourages generalized awareness, and what is cultivated will likely differ.