What is the term for a collective name for letters, digits, and symbols?

The term that refers to a collective name for letters, digits, and symbols is "alphanumeric." This term specifically encompasses both alphabetic characters (letters) and numeric characters (digits). When we refer to alphanumeric data, we are usually discussing any combination of letters (both uppercase and lowercase) along with numbers (0-9), and often include symbols like punctuation marks as well.

The other options do not accurately represent the entire set of characters as described in the question. For example, while "character set" refers to a complete set of characters that can be used in a computer system, it is a broader term that does not specifically emphasize the combination of letters and digits. "Symbolic" typically pertains more to symbols in a general sense, without explicitly including alphanumeric aspects. Finally, "lexicon" generally refers to the vocabulary of a language rather than a collection of characters or symbols used in computing. Therefore, the alignment of "alphanumeric" with letters, digits, and symbols highlights its correctness in this context.