dictionary attack is a slightly more sophisticated example of a brute-force attack.
This uses an automated process of loading a list of frequently used passwords and phrases into a computer system until something fits.
Most of the dictionaries will be composed of credentials from previous hacks, although they will also contain the most common passwords and phrases.
This technique takes advantage of the fact that many people will use catchy phrases as passwords, which are usually whole words glued together.
This is largely the reason why systems will strongly recommend the use of several types of characters when creating a password.