You surely know what a password is. When accessing private data on a protected system, you need a password (sometimes also called passphrase) and most often a username to tell the system your identity.

Most things about passwords have already been said, but some things cannot be repeated too often.

1. Do not tell your passwords to anyone. If you are asked by anyone to tell them your password, say no. There simply is no reason. If someone tells you he is an admin and needs to know your password, he is lying.
2. When choosing your password, do not choose something that others could simply guess. Do not use the name of your spouse or cat, or the company name printed on your computer or monitor. While the best thing would be a random string of characters and numbers and even special characters, if you really need something that is easy to remember, take parts of words and combine them into something that you can still speak, but that gives no sense. Attach a few numbers to it to be on the safer side.
3. Do not write your password down on a sticky attached to your screen, or anywhere on your workspace. If you need to write it down, put the paper with it into your wallet, but never anywhere near the computer.
4. Do not save a file with all your passwords on your computer. If you cannot remember them all, write them down. If you really want to save them in a file, encrypt that file.