Encryption is the process of protecting data by using an algorithm to scramble it.
This manual will be talking about local file encryption – that is, encrypting files on a hard drive (or encrypting the entire hard drive; more on that later).
The files are safe as long as they are kept in the encrypted area.
TrueCrypt is a free, cross-platform program (meaning that it works in Windows, Mac OS X and Linux distributions including Ubuntu) that you can use to encrypt your data.
It is classified as “On The Fly Encryption” (OTFE) software, which basically means that it encrypts and decrypts files as you access and modify them and that all files within the area of encryption are available as soon as you enter the key.