These four terms are often confused by learners. Eggplant (also called aubergine in British English) is a large purple vegetable with a spongy inside, eaten cooked. Courgette (British) or zucchini (American) is a long green summer squash with a firmer texture, eaten raw or cooked. Brinjal is the word for eggplant used in Indian, Pakistani, and Singaporean English. In Taiwan, 茄子 (eggplant) is the everyday term; English menus use eggplant or aubergine depending on the restaurant's style. Think of it this way: if it is large, purple, and soft when cooked, it is eggplant. If it is long, green, and crunchy, it is a courgette or zucchini.
The word 'eggplant' first appeared in English in the mid-1700s. It combines 'egg' and 'plant' because early varieties grown in Europe had white, egg-shaped fruits that looked like chicken eggs. The botanical name is Solanum melongena, and the plant is a member of the nightshade family, which also includes tomatoes and potatoes.