A very simple definition is that Buddhism is the practice of living our lives in as realistic, and compassionate a manner as possible, by understanding the true nature of life as described in The Four Noble Truths. We do this by following the lessons from the Buddha himself, who understood how we make our lives unnecessarily difficult due to our distorted perceptions of reality.
In Buddhist practice, there are two forms of meditation. One is the development of mental concentration, (samatha meditation). Samatha meditation involves focusing the mind on a single object in order to develop stillness of mind. The other form of meditation is Vipassana (insight meditation). Insight meditation is practiced in order to inquire into the true nature of our self, and it leads to personal freedom. Buddhist meditation aims at purifying the mind, enabling one to develop the wisdom which realizes the true nature of life.