Chai (often specifically "Masala Chai") is a spiced tea beverage, typically made with black tea, a blend of aromatic spices (like cardamom, ginger, cloves, cinnamon, and black peppercorns), milk, and a sweetener. Its unique blend of spices sets it apart.
Interestingly Chai is just 'tea' in Hindi, so when you ask for a Chai Tea, you're just asking for a 'tea tea' :)