What is hashing in terms of data security?

Hashing in terms of data security refers to the use of an algorithm to take an input (or 'message') and produce a fixed-size string of characters, which is typically a sequence of numbers and letters. This output is known as a hash value or hash code. The primary purpose of hashing is to ensure data integrity, allowing users to verify that data has not been altered or corrupted.

When data is hashed, it transforms the original data into a unique hash value that cannot be feasibly reversed to reveal the original data. This makes hashing particularly useful for storing passwords, creating digital signatures, and ensuring data integrity in various applications. Since even a small change in the input will lead to a drastically different hash output, it serves as an effective way to detect changes in data.

In the context of the other choices, the process of encrypting data using a key is distinct from hashing, as encryption is reversible. Storing data in a database and data compression do not involve generating a unique, fixed-size output directly related to the original data in the way hashing does. Thus, the understanding of hashing as an algorithmic mapping is its defining feature in the realm of data security.