Encryption of a message means the information in it is hidden so that anyone who’s reading (or listening to) the message, can’t understand any of it unless he/she can break the encryption. An original plain message is called plaintext and an encrypted one cryptotext. When encrypting you need to have a so-called key, a usually quite complicated parameter that you can use to change the encryption. If the encrypting procedure remains unchanged for a long time, the probability of breaking the encryption will in practise increase substantially. Naturally different users need to have their own keys, too.