In Jainism, the basic unit of matter is called Paramāṇu (परमाणु).

• Paramāṇu is the smallest indivisible unit of Pudgala (matter).
• Many paramāṇus combine to form skandha (a material aggregate).
• In Jain philosophy, Pudgala is one of the six substances (dravya), and it has form, touch, taste, smell, and color.

So, in simple words:

Matter = Pudgala Smallest basic unit of matter = Paramāṇu

If you want, I can also explain the Jain classification of matter in simple terms.