What is encrypted field in salesforce?

Encrypted fields are stored with additional security on our servers, so they're ideal for fields that are collecting extra-sensitive data. 

Encrypted data can only be read by a machine with a specific key and password that we keep hidden and protected, so if the data were to be compromised it could not be read.

Ex: Aadhar Number 

4563 7687 xxxx

Encrypted numbers are denoted with XXXX .encrypted numbers are case-sensitive information.