The word "dru" is the root word that constitutes dravya. Dravya is anything, everything that divides, combines and flows through a set of changes in due course of time. In all the things that surround us these characteristics exists and hence everything fall under this category. Definition
Guna and karma have their dwelling in dravya. It is the essential factor (samvayi karana) of other karya dravya and the survival of guna and karma is possible only if dravya exists.

Classification of dravya
Categorically dravya can be divided in two divisions:

Karan dravya
The dravya that is responsible for the creation and cannot be fragmented further or destroyed is called karna dravya. It consists of nine dravyas.

Karya dravya
It owes its origin to karan dravya as it is instituted by the appropriate combination of karan dravya. This type of dravya is destructible and has a short span to function. After it is destroyed, karya dravya merges into its karan dravya.