What is the right word used to describe the actual taste of tasting a green mango?

The right word to describe the taste of a green mango is "tart" or "sour." Green mangoes are not fully ripe and therefore have a more tangy and sour flavor compared to ripe mangoes.

Define them?

"Tart" is a taste sensation often associated with acidic or sour foods. It is a flavor that is sharp, acidic, sour, or tangy, and can create a puckering sensation in the mouth. "Sour" is also a taste sensation characterized by the presence of acids, such as citric acid or acetic acid. Sour foods have a sharp, tangy taste that can stimulate the saliva glands and create a mouth-puckering sensation. In the case of a green mango, the taste may be a combination of tartness and sourness due to its unripe nature.