A Hash is a dictionary-like collection of unique keys and their values. Also called associative arrays, they are similar to Arrays, but where an Array uses integers as its index, a Hash allows you to use any object type. You retrieve or create a new entry in a Hash by referring to its key.
As more secure web services avoid storing passwords in plain text format, languages such as PHP provide various (undecryptable) hash functions to support the more secure industry standard. This topic provides documentation for proper hashing with PHP.