Something small that opens something big, like a door or a password. Keys are meant to provide physical or network security, although physical locks may often be picked and simple passwords guessed. In computers, a key is usually a small phrase or word that opens something big such as an e-mail, Web page, or gives access to your computer.
Vulnerability: A variety of attacks can be used to gain access to keys and the contents they secure. Social engineering, for instance can trick someone into handing over the keys un-intentionally. This trick most often occurs froms someone posing as an official source. However, keys can be eavesdropped without making measures to keep it secret. Measures to ensure secrecy often include cryptography.
Creation: Some keys are created simply by typing in a fresh password when prompted. Some passwords are created by more than one person or source, for instance by the CEO and CFO of a company to digitally sign a contract. Some keys are public keys that are exchanged freely. These "public" keys do not themselves decrypt information but instead are connected with a private key with individual password.