1. In hacking circles, a dictionary is simply a list of words that plug into cracking programs in order to break passwords. Such dictionaries not only contain real words, but words that people choose for passwords (example: NCC1701, which is the serial number for the starship Enterprise in Star Trek). Key point: It takes only a couple minutes to run through hundreds of thousands of words in a dictionary in order to crack a password. Therefore, never choose a word that may be in a dictionary. Key point: The dictionary files that hackers use are not necessarily the same as English dictionaries. In theory, users will choose the same passwords they have used before, and unrelated users will choose the same passwords. Therefore, lists of passwords users chose in the past forms a key component of hacker dictionaries. Key point: Hackers also run non-English dictionaries, so choosing foreign words isn't a good defense. From Hacking-Lexicon