(verb) make or keep in contact with someone
I’ll start the first part of the project, you start the second, and drop me a line in a few days.
Student 1: I am going back to Brazil.
Student 2: I am going back to Korea.
Student 1: Good luck to you! I hope we will meet again soon!
Student 2: Drop me a line!
The boyfriend is always dropping his girlfriend a line while they are separated.
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