drop in

drop in

To visit one casually and/or unexpectedly. Drop in whenever you want—I'll be home all day.
See also: drop

drop in(to) (something)

1. To let go of something so that it enters something else. In this usage, a noun or pronoun can be used between "drop" and "in" or "into." Oh, I just dropped my donation into the box outside.
2. To fall into something. Sean positioned himself so that the fly ball just dropped into his glove.
See also: drop
Farlex Dictionary of Idioms.

drop in (on someone)

 and drop in (to say hello)
to pay someone a casual visit, perhaps a surprise visit. I hate to drop in on people when they aren't expecting me. You're welcome to drop in at any time.
See also: drop
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

drop in

v.
1. To let something fall into some other thing: I dropped some spare change in the beggar's cup. I took some rocks to the hole and dropped them in. Don't push the latch down into the lock; just let it drop in.
2. To come to some place for a casual visit: We'll drop in and see how you're doing tomorrow. Should we drop in on our neighbors tonight?
See also: drop
The American Heritage® Dictionary of Phrasal Verbs.
See also:
  • drop in(to) (something)
  • drop over
  • drop in for a chat
  • drop out of
  • drop out of (something)
  • drop it
  • Drop it!
  • fond of a drop
  • drop round
  • drop (one) a few lines