Password spraying is a form of password brute-forcing attack. In password spraying, an attacker (with the help of a tool) cycles through a list of possible usernames (found using OSINT techniques against a target company or other means) with a couple of most commonly used weak passwords.
In comparison, a traditional brute-force works by selecting a username from the list and trying all the passwords in the wordlist against that username. Once all passwords are exhausted for that user name, another username is chosen from the list and the process repeats.