Being mindful means being aware of what you are doing and what is in your immediate environment. Often, we are not mindful, which means that instead of focusing on what we are directly experiencing, our mind wander off elsewhere. I may be eating a delicious meal, but not noticing the flavours; instead, I am off worrying about a project I have due in the next week. I may be watching a great movie, but instead I’m off worrying about my illness of some kind, etc.
Mindfulness means doing what you are doing with full attention. To eat mindfully, for instance, means just (without distraction) and fully (with full attention) eating. I notice the texture of my fork and of each bite of food. I notice its colours. I notice the many different subtle flavors in the dish. I notice the feeling of it going through my mouth and down my throat and the feeling of getting more full and less hungry. I feel the warmth and pleasure of eating the food, etc. This is mindful eating.
We can do anything mindfully in this way. When I watch a movie mindfully, for example, what I am doing is fully and only watching the movie. I’m not thinking of anything else. I’m immersed in the movie, in its sounds, in its colours, in its stories, in its characters, in its camera angles and cinematic techniques, etc.
To summarize: doing something mindfully means doing it with full attention and not letting your mind wander off into other things. Stated differently, mindfulness is just and fully doing what you are doing and not getting lost in thoughts about other things.