Simply: A hash is a function that converts one value to another. It's a string of numbers and letters, produced by hash functions. Even a small change in a string creates a completely new hash.

Detailed: A Hash Value (also called as Hashes or Checksum) is a string value (of specific length), which is the result of calculation of a Hashing Algorithm.
​
Hash Values have different uses. ... When Data is fed to MD5 Hashing Algorithm, it generates a 128-bit Hash Value String as a 32 digit hexadecimal number.