Some have viewed mindfulness as a mental state, while others have viewed it as a set of skills and techniques.
A distinction can also be made between the 
state of mindfulness and the 
trait of mindfulness.
 According to David S. Black, whereas "mindfulness" originally was 
associated with esoteric beliefs and religion, and "a capacity 
attainable only by certain people",
 scientific researchers have translated the term into measurable terms, providing a valid operational definition of mindfulness.
 Black mentions three possible domains:
- A trait, a dispositional characteristic (a relatively long lasting trait), a person's tendency to more frequently enter into and more easily abide in mindful states;
 
- A state, an outcome (a state of awareness resulting from mindfulness training), being in a state of present-moment awareness;
 
- A practice (mindfulness meditation practice itself)
 
Various definitions
- Trait
 
- "A quality of consciousness manifest in, but not isomorphic with, the activities through which it is enhanced."
 
- State
 
- "A kind of nonelaborative, nonjudgmental, present-centered awareness
 in which each thought, feeling, or sensation that arises in the 
attentional field is acknowledged and accepted as it is"
 
- Practice
 
- "Mindfulness is a way of paying attention that originated in Eastern meditation practices
 
- "Paying attention in a particular way: on purpose, in the present moment, and nonjudgmentally"
 
- "Bringing one’s complete attention to the present experience on a moment-to-moment basis"
 
Two-component model
In a paper that described a consensus among on an operational and testable definition, Bishop, Lau, et al. (2004)
 proposed a two-component model of mindfulness:
The first component involves the self-regulation of attention so that
 it is maintained on immediate experience, thereby allowing for 
increased recognition of mental events in the present moment. The second
 component involves adopting a particular orientation toward one’s 
experiences in the present moment, an orientation that is characterized 
by curiosity, openness, and acceptance.
In this two-component model, self-regulated attention (the first component) "involves bringing awareness
 to current experience - observing and attending to the changing fields 
of "objects" (thoughts, feelings, sensations), from moment to moment - 
by regulating the focus of attention". Orientation to experience (the 
second component) involves maintaining an attitude of curiosity about 
objects experienced at each moment, and about where and how the mind 
wanders when it drifts from the selected focus of attention. Clients are
 asked to avoid trying to produce a particular state (i.e. relaxation), 
but rather to just notice each object that arises in the stream of consciousness.
"Wiki" thanks to Yassolmolook
I wonder whether I can enhance this trait for the sake of happier life..