heres the wiki about it
Tathata (Sanskrit तथाता tathātā; Chinese language 眞如 pr.: zhēnrú /chen-ju; tib. de bzhin nyid; kor. 진여, jinyeo; jap. 真如, shinnyo; viet. chân or chơn như) is variously translated as "thusness" or "suchness". It is a central concept in Buddhism as well as the Hindu Upanishads; in the latter, it is used to refer to Brahman. The synonym dharmatā is also often used.
One of the synonyms of the word Buddha is Tathagata, which means "thus gone" or "thus come". Tathata as a central concept of Mahayana Buddhism, expresses the appreciation of reality within a unique moment. As no moment is exactly the same, each one can be savored for what occurs at that precise time. Tathata is often best revealed in the mundane, such as noticing the way the wind blows through a field of grass, or watching someone's face light up as they smile. Shakyamuni Buddha transmitted the awareness of Tathata directly to Mahakasyapa in what has come to be rendered in English as the Flower Sermon. As Molloystates, "We know we are experiencing the 'thatness' of reality when we experience something and say to ourselves, 'Yes, that's it; that is the way things are.' In the moment, we recognize that reality is wondrously beautiful but also that its patterns are fragile and passing."
The term Tathata in the Mahayana tradition is seen as representing the base reality and can be used to terminate the use of words. A 5th century Chinese Mahayana scripture entitled "The Awakening of Faith in the Mahayana" describes the concept more fully: "In its very origin suchness is of itself endowed with sublime attributes. It manifests the highest wisdom which shines throughout the world, it has true knowledge and a mind resting simply in its own being. It is eternal, blissful, its own self-being and the purest simplicity; it is invigorating, immutable, free... Because it possesses all these attributes and is deprived of nothing, it is designated both as the Womb of Tathagata and the Dharma Body of Tathagata
now for the theravada POV>>>