Paying attention to the downright fucking obvious. This usually manifests as paying for a therapist to tell you that if you fart you might need to shit soon. Can only be counteracted by a whack over the head with a plank and a tattoo reading, 'GET A FUCKING GRIP.'

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

Popular ideas of Mindfulness:
1. Meditation watered-down to one ultra-simple practice: noticing what your mind is thinking, without judging the thoughts. Similar to stream of consciousness, but at least paying attention to the idea that "My mind is thinking this."
2. Doing things undistractedly; paying attention to what we are doing.

Traditional Buddhist definition:
3. Part of our mind which holds and remembers the meditation object, or enables us to remember things. It also helps to overcome distraction. If we are very forgetful or get distracted easily, then we need to strengthen this kind of mindfulness. In traditional Buddhist meditation, one focuses on a feeling or concept, and tries to hold the attention on this feeling or concept with mindfulness.

a state of being in the ultimate form of existence in terms of your mind exceeding your physical body.