Uppercase refers to the larger form of letters used in writing, often called capital letters. These letters are typically used at the beginning of sentences, for proper nouns, and for emphasis. For example, in the word Apple, the letter "A" is uppercase, while the rest of the letters are lowercase. In typography, uppercase letters are distinct from lowercase letters, which are smaller and often have different shapes. The use of uppercase can affect the readability of text and is an important aspect of grammar and style in written communication.