Letter case refers to the distinction between uppercase and lowercase letters in writing. Uppercase letters, also known as capital letters, are typically used at the beginning of sentences or for proper nouns, such as names and places. Lowercase letters are used for most other text, making it easier to read and understand. In digital communication, letter case can affect the tone of a message. For example, using all uppercase letters can be interpreted as shouting, while all lowercase may seem informal. Understanding letter case is essential for effective writing and clear communication in various contexts, including emails and social media.