A tea cake, in British usage, is a light, yeast-leavened bun containing dried fruits such as currants, split, toasted, and buttered before serving with tea; despite the name, it is a bread rather than a cake. In American usage, 'tea cake' instead refers to a small, sweet, cookie-like baked good, closer to what the British would call a tea biscuit or tea cookie.
The British teacake is associated with the north of England, where it remains a staple of cafes and tea rooms; it is typically 3-4 inches across, with a smooth top and a lightly spiced, mildly sweet dough. The American tea cake is smaller and drier, closer in size and texture to a shortbread or sugar cookie, and is usually served plain or lightly glazed rather than toasted and buttered.
Both styles are meant to be eaten alongside a cup of tea rather than as a standalone dessert, and both can be varied with additions like citrus zest, spices, or nuts.