1. What is Complexity?

Complexity is the Measurement of Analysis of Algorithm.

2. What is Hashing?

In terms of Database, Hashing is a method of sorting and indexing data. The idea behind hashing is to allow large amounts of data  to be indexed using keywords or keys commonly created by complex formulas. Hashing allows for a large amount of information to be searched and listed.

In terms of  security, hashing is a method of taking data, encrypting it, and creating unpredictable, irreversible output. There are many different hashing algorithms. MD2, MD5, SHA, and SHA-1 are examples of hashing algorithms.