Mindfulness is focusing on one thing in the present moment. It is to simply allow oneself to experience the activity of the moment while excluding worries, self-doubts, and distractions. Mindfulness is non-judgmental, avoiding opinions of good or bad. It is also effective, focused on what works, rather than what is right or wrong.
Achieving this focus requires practice, in order to gain control of attention. The skill of mindfulness involves observing and describing on purpose, in a particular way.