You just have to look it up anywhere on the web or the dictionary. Matter is a philosophical category, denoting the outside world (outside of our perceptions of it), which is independend of our mind. It therefore denotes an objective reality which exists on it's own and outside of our mind, and is not dependend of our awareness or mind. This objective reality is reflected within our mind through our perceptions. Materialism, in contrast to Idealism, states that matter is primary, and consciousness is secondary. Matter is not distinguishable from motion/change. Nowhere and at no time can matter exits without motion or change, and motion or change can not exist without matter. Motion/change is the way in which matter exists. Note: Please distinguish the philosphical term 'matter' from the physical term 'matter'. In physics, matter is to be thought of as particles, which behave like point-masses, in contrast to light or radiation (photons and neutrinos). The philosophical term matter covers all forms of physical entities, including massive particles, energy, radiation, fields, etc.