BCD stands for

Concept

Digital circuits operate purely in binary, but humans and displays read decimal digits, so digital systems need a bridge code that lets each individual decimal digit (0–9) be represented by its own small group of bits. The most common such bridge is the 8421 weighted code, universally called BCD.

Application

The acronym names exactly this scheme: “Binary” is the base-2 alphabet the bits are drawn from; “Coded” is the digit-by-digit encoding process; “Decimal” is the base-10 digit that actually gets encoded. So BCD = Binary Coded Decimal. For example, decimal 47 is stored in BCD as 0100 0111 (4 → 0100, 7 → 0111) — two separate 4-bit groups, one per decimal digit — unlike the plain binary form of 47, which is the single pattern 101111.

Cross-check / contrast

Each remaining option swaps out one of the three words for a near-miss term that breaks the standard name:

• “Binary Coded Digit” replaces the number-system name with the generic word “digit,” which does not identify which base is being represented, so it cannot correctly complete the term.

• “Bit Coded Decimal” replaces the number-system name with “bit” — a single storage unit, not the name of a number system — so it misnames the first word of the acronym.

• “Bit Coded Digit” makes both substitutions at once, combining the errors of the two options above.

Binary Coded Decimal is therefore the term BCD stands for.