Mindfulness comes from the Sanskrit and Pali words for "to remember" and "clear comprehension". It is the ability to calmly concentrate and attend to the present, to what is.
"The "what is" is what you are, not what you would like to be; it is not the ideal because the ideal is fictitious, but it is actually what you are doing, thinking, and feeling from moment to moment. 'What is' is the actual, and to understand the actual requires awareness, a very alert, swift mind."