Mindfulness is a practice found within multiple therapy approaches in which one learns to focus on the present moment. It is a process of acceptance, non-judgment, and gentle curiosity for whatever may arise. As the mind naturally drifts toward future planning and worries, or past frustrations and hurts, we kindly notice our minds have drifted and return to the present by way of a chosen focal point - often one's breath. One may also choose to gently explore, observe and "be with" whatever sensations, thoughts, feelings and memories arise, while aware they are still grounded in the present moment.
Mindfulness assists us to recognize that the source of much of our suffering is our dwelling in a future that hasn't happened, or a past that can't be changed. Mindfulness focuses on the power of presence, the only moment that truly is.