An attack using every possible input to attempt to produce the correct output. Typically the method of last resort when no weakness allows the use of a more restricted input set. E.g. trying all possible (or likely) passwords, in an attempt to guess the correct one.
I have an issue with Hydra when i use it. First let me inform that, i read multible guides, tries the excact same command lines as in guides directly supported by the Damn Vulnerable Web Application ...