Paper size refers to the dimensions of a sheet of paper, which can vary based on regional standards. Common sizes include A4, which measures 210 x 297 mm, and Letter, measuring 8.5 x 11 inches. These sizes are used for various purposes, including printing documents, creating flyers, and crafting. Different countries have their own paper size standards. For example, the ISO 216 standard is widely used in Europe and other parts of the world, while the ANSI standard is common in North America. Understanding paper sizes is essential for selecting the right paper for specific tasks.