Meaning of “drop” - Learner’s Dictionary

drop

noun us uk /drɒp/
She dabbed a drop of perfume behind her ears.Huge drops of rain were falling from the sky.There were drops of blood on the floor.Mix two drops of lavender oil with two drops of lemon oil.Drops of water fell off the leaves.
LIQUID [ C ]

B1 a small, round-shaped amount of liquid:

I felt a few drops of rain.
REDUCTION [ no plural ]

B2 a reduction in the level or amount of something:

There has been a drop in crime recently.
SMALL AMOUNT [ no plural ]

a small amount of a liquid you can drink:

Would you like a drop more milk?
DISTANCE [ no plural ]

a vertical distance down from somewhere to the ground:

It's a drop of about 50 metres from the top of the cliff.

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