Index cards are small, rectangular pieces of card stock, typically measuring 3 by 5 inches or 4 by 6 inches. They are commonly used for organizing information, taking notes, or creating flashcards. People often write down key points, definitions, or reminders on these cards for easy reference and study. These cards can be used in various settings, such as classrooms, offices, or at home. They are especially popular among students and educators for study techniques and project organization. Index cards can also be stored in boxes or card files, making them a convenient tool for managing information efficiently.