The abbreviation "ROM" stands for "Read-Only Memory." In this context, the letter 'R' in "ROM" expands to "Read."

Here's a detailed explanation:

1. ROM Explanation: In computing, ROM is a type of non-volatile memory. It is primarily used in the computer system to store firmware or software that is closely tied to specific hardware. The content of ROM can only be read and not written, hence the term "Read-Only Memory."
2. Meaning of Read: The operation "read" in memory terminology implies accessing or retrieving data from a storage medium, in this case, the ROM. Unlike RAM (Random Access Memory), which allows both read and write operations, ROM restricts users to read the data, which confirms the purpose and functionality of ROM in maintaining system data that doesn't change frequently.

Let's analyze each option to understand the correct choice:

• Random: This term is associated with RAM (Random Access Memory), which is incorrect in the context of ROM.
• Ready: While this term fits some components of computing, it's not applicable for ROM.
• Read: This is the correct term, as explained earlier. ROM allows data to be read but not modified.
• Referencial: This term does not relate to ROM.

Therefore, the expanded form of the letter 'R' in the abbreviation "ROM" is "Read."