Dhamma (Dharma)
On occasions, the Buddha would explain Dhamma to His disciples, often giving discourses on the subject. Sometimes, He would just twirl a flower. Sometimes, He would simply maintain Noble Silence.
Dhamma is everywhere. It is simply 'the way it is'; the Truth. Everything, every system in the universe, from the (apparent) 'emptiness' of space to supernova and black holes, is a manifestation of Dhamma. Even the way that sub-atomic particles dance is Dhamma. Such particles do not dance in response to some unwritten cosmic dictate to 'obey the rules'. The dancing particles are themselves Dhamma.
The Buddha taught that to be Enlightened is to be at one with 'Dhamma'. To understand Dhamma 'as it is' requires a stilled and one-pointed mind. These are the very qualities that meditators develop over time. This is why the Buddha always emphasised the vital importance of Meditation for His followers. A full and complete Understanding of Dhamma can't be achieved just by reading books about Dhamma; the Truth is beyond words.