Madhyamaka (Sanskrit: मध्यमक, Madhyamaka, Chinese: 中觀派; pinyin: Zhōngguān Pài; also known as Śūnyavāda) refers primarily to a Mahāyāna Buddhist school of philosophy founded by Nāgārjuna. The school of thought and its subsidiaries are called "Madhyamaka"; those who follow it are called "Mādhyamikas". According to Madhyamaka all phenomena are empty of "substance" or "essence" (Sanskrit: svabhāva) because they are dependently co-arisen. Likewise it is because they are dependently co-arisen that they have no intrinsic, independent reality of their own.

Whatever is dependent arising
We declared that to be emptiness.
That is dependent designation,
And is itself the middle way.

—Nāgārjuna, Mūlamadhyamakakārikā 24:18

Read more about Madhyamaka:  Origins and Development, Schools, Concepts, Understanding in Buddhist Tradition, Understanding in Modern Scholarship