Passwords are not stored in plain text in your computer. Instead they are hashed. A hash is a one way cryptographic process, meaning that your plain text is encoded into a hash but there’s no way to reverse the hash to recover the plain text password.
A brute force attack would be a continuous trial and error attempt to guess the password that produces the same hash.
Most accounts will lockout after a certain number of failed attempts in order to mitigate brute force attacks.
An offline brute force attack is when the malicious attackers get a hold of the password hash file and then can perform a brute force attack without being locked out after a certain number of failed attempts.
