Key stretching
Making every password guess expensive by running a function thousands or millions of times.
A human password has little entropy, so it can be tested against billions of candidates per second on a GPU. Key stretching counters this by running a function over the password and a salt many times, so each guess costs the attacker as much time as it costs the legitimate user. PBKDF2, bcrypt, scrypt and Argon2 all do this. The newer ones also demand memory, which is harder to parallelise on a GPU.
Stretching is no substitute for a good password. It raises the cost per guess, but does nothing for "hunter2", however many rounds you run.