To write your phone number down and

A.) leave it in something inconspicuous so as to let someone whom you find attractive find it and call you

or (less commonly)

B.) literally drop it somewhere allowing anyone who finds it to contact you.
Example 1:

Person A: Last night I wrote my number down on a scrap of paper, folded it into a 5 dollar bill and gave it to the waitress that i wanted to hit on.

Person B: You dropped a number?

Person A: Why not, she was a hot red-head?

Example 2:

Person A: I like dropping my number because it's easier to meet new people who you only talked to in passing.
by TheLogicist April 3, 2011
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As you know, when you go to the bathroom it's either #1 or #2. Dropping numbers refers to doing #2.
Michael will be right back. He's in the bathroom dropping numbers. OR , I'm about to go drop some numbers.
by Msimeoni May 21, 2015
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In gang conflicts if you turn an enemy's friends against him he has no strength in number and there won't be much if any retribution in response to giving him a green light.
Tommy is as good as dead. Los Locos Vatos dropped his numbers (dropping numbers) and now he's on the hat for all the work he put in against them!
by raptor5000 April 2, 2018
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