Biometrics
Biometrics are a system which analysis characteristics such as a fingerprint or face scan to unlock a system, a username and password is usually alot safer but some people prefer the usually easier to use interface of a biometric scan but on the other and biometrics can malfunction and shut you out for good - most of the time there is a backup username or password but it is still an inconvenience. The most common examples are things like fingerprints - face scans and the all time movie favorite retina scans. The advantages of this are that sometimes it can be easier and you wont have to go through the hassle of remembering passwords and or having to go through the painful torture of password recovery! However there are some disadvantages, for example biometric scans might not work first time and they can lock you out for good - furthermore they can break easily and leave some very unhappy people stuck out of what they are trying to get into.
Digital signature
A digital signature is an encrypted code attached to a particular document to verify its contents and the senders and receivers identification.