Octal is a base-8 numeral system that uses digits from 0 to 7. It is commonly used in computing and digital electronics because it can represent binary numbers more compactly. Each octal digit corresponds to three binary digits (bits), making it easier to read and write large binary values. In octal, the place values are powers of 8, similar to how decimal uses powers of 10. For example, the octal number 17 represents 1 \times 8^1 + 7 \times 8^0, which equals 15 in decimal. Octal is often used in programming and file permissions in systems like Unix.