Bruteforce is a type of cyber attack in which an attacker submit multiple combination of passwords or phrases in the hope of any combination matching correctly.This type of attack is mostly useful to crack the weak passwords.
Understanding it through an example:
Suppose here an attacker tries to crack the password of an user. The attacker uses here a file that contains millions of words that can be used as a password. The attacker tries these passwords one by one for authentication. If this file contains the correct password, the attacker will get access to the user account.
Have you ever noticed? that most of the websites ask you to use the password in the combination of letter and numbers and more than 6 or 8 characters in length. It is because the more the password will be longer and in the combination of letters , symbols and numbers , the more it will be time consuming and difficult to perform bruteforce attack.
Many websites nowadays are using this technique in order to be prevented from bruteforce attack.In this technique the websites sets the limit for entering wrong passwords or pins.If the attacker exceeds the limit then his/her ip will be blocked or in some cases the users account got informed and locked in order to prevent from the authorization of attacker.
Last but not the least , use of two factor authentication. It is recommnded every users to use two factor authentications for the login in any websites.In two factor authentication , even if by any luck or chance the attacker get success to guess user password, after entering the password , he/she will face another authentication to verify its login.