At the heart of it, meditation is simply the practice of paying attention to what we are doing while we are doing it, whatever this may be. In the Buddhist tradition, this type of attention is called mindfulness.
Traditionally we have come to think of meditation as sitting on a cushion in the lotus position, but this is simply one form of meditation. Instead, meditation is the patient process of settling our mind in the present moment so that we are fully engaged with whatever we are doing at that moment; and consequently it can apply to all aspects of our lives. For example, when we eat meditatively, we are fully present with eating, instead of eating with our mouth and planning the rest of our day with our minds.
To become proficient at meditation, we learn to identify and work with distraction, which is the tendency of the mind to drift off into thoughts and daydreams. Distraction disconnects us from the present moment. So, in meditation, every time our attention gets lost, we notice this and return it to the focus of our meditation. This is done gently, just as a good parent gently returns a wandering child back to where he should be. And it is done patiently, again and again, until our mind naturally comes to rest of its own accord in the present moment.
As we become competent at meditation, it stabilises our mind and innate qualities of wisdom and compassion start to reveal themselves to us. From here they permeate all aspects of our lives. We begin to understand how things are not as solid and unchanging as we'd first thought, and how our lives are interrelated with those of all other living things. Out of this realisation comes a sense of great joy and freedom. We find ourselves appreciating our lives more and more and living more intensely in the present moment. As we do so, our vision expands to encompass not only our own happiness but also that of all other beings.