Meaning of “knock” - Learner’s Dictionary

knock

verb us uk /nɒk/
I knocked several times but no one answered.She knocked on his bedroom door and left the tray outside.She walked up to the door and knocked.Helen knocked and entered.He walked up to the house and knocked at the front door.
MAKE NOISE [ I ]

B1 to make a noise by hitting something, especially a door, with your closed hand in order to attract someone's attention:

There's someone knocking at/on the door.
Please knock before entering.
HIT [ T ]

B1 to hit something or someone and make them move or fall down:

He accidentally knocked the vase off the table.
I knocked over the mug.
He was knocked unconscious by the blast.
CRITICIZE [ T ] informal

to criticize someone or something, often unfairly:

She knocks every suggestion I make.

(Definition of “knock verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)