Hydra is a password guessing (cracking) tool that can be used in a wide range of situations, including with the forms-based authentication commonly used in web applications. It is a quick and stable network login hacking tool which uses dictionary or brute-force attacks to try several passwords and login combinations against a login page.
Of course, you can use a tool such as Burp Intruder to perform any attack of this kind in a fully customized process, however, in many conditions. Hydra can be just as useful.
Hydra enables you to specify the target URL, the relevant request parameters, word lists for attacking the username and password fields, and details of the error message that is returned following an unsuccessful login. The (-t) setting can be used to specify the number of parallel threads to use in the attack.
This tool makes it possible for researchers, hackers and security consultants to show how easy it would be to gain unauthorized access to a system remotely.