Explanation:

The process of representing characters (like letters, numbers, punctuation) and symbols in a digital format, typically using sequences of bits grouped into bytes, is known as a coding system or character encoding. Examples include ASCII, EBCDIC, and Unicode, which assign unique numerical codes to characters. Option (d) Coding system is correct. Option (a) Number system refers to how numerical values are represented (e.g., binary, decimal). Option (b) Alpha system is not a standard term. Option (c) Byte system is vague; while characters are stored in bytes, this doesn't describe the method of representation, but rather a unit of storage.