Hex Hexadecimal
Number system with base 16 — digits 0–9 + letters A–F. Each hex character represents 4 bits (nibble), two hex characters = one byte. Compact way to show binary data.
Universal prefix: 0x (C family), # (CSS colors), $ (Motorola), suffix h (Intel). HTML/CSS colors: #FF5733 = (255, 87, 51) RGB. Memory addresses in debuggers, hex editors, hash values — all in hex. Octal (base 8) is a historical curiosity remaining in Unix file permissions (chmod 755). Binary (base 2) is rarely used directly in code, but often in bitmasks.