What does Read-only mean?
Read-only is a designation for any object or construct which can no longer be altered after creation, it can only be read.
This can refer to both hardware and software constructs such as read-only memory chips like BIOS and CMOS and CD/DVD/Blu-ray-ROMs for hardware, and read-only files for software constructs. In either case the contents of the object when marked as read-only can no longer be changed, only accessed or read.
Techopedia explains Read-only
Read-only is a status which indicates that something is unalterable, capable of being read but not written or overwritten.
In software, read-only is a safety measure which protects files and data from accidental or intentional alteration or deletion and may be imposed only for select users or groups of users. This means that some users see the files as read-only while others are allowed to alter or delete it; this is widely used for permissions and security purposes.
The number one benefit of read-only constructs is consistency. Since they cannot be changed or even then can only be changed in certain circumstances and by certain individuals, we can ensure the consistency of the data or the operation of a piece of hardware and less prone to errors due to unexpected changes.