Clock.tick() not functioning

So I want to make a python game using pygame, and i want to set my fps as 60 but it comes out with an error.

Here is code:

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            exit()
    pygame.display.update()
    clock.tick(60) 

Here is error:

  File "/Users/...", line 14, in <module>
    clock.tick(60)
NameError: name 'clock' is not defined

Why is this happening???