Definition of "drop in"

drop in

verb
third-person singular simple present drops in, present participle dropping in, simple past and past participle dropped in
1. (idiomatic) To arrive casually and unannounced, with little or no warning; also, to visit without an appointment.
  Quotations
  We made an odd party before the arrival of the Ten, particularly when the Celebrity dropped in for lunch or dinner.
  1897 December (indicated as 1898), Winston Churchill, chapter V, in The Celebrity: An Episode, New York, N.Y.: The Macmillan Company; London: Macmillan & Co., Ltd.
  And so you felt like droppin’ in and just expect me to be free / Well, now I'm saving all my lovin’ for someone who's lovin’ me
  1978, Dino Fekaris, Freddie Perren (lyrics and music), “I Will Survive”, in Love Tracks, performed by Gloria Gaynor
2. (surfing) To paddle into and take off on a wave another surfer is already riding.
  Quotations
  Most beginners are blissfully unaware that dropping in on someone is a cardinal sin.
  2003, Neal Miyake, “The Unwritten Rules of Surfing”, in (Please provide the book title or journal name)‎, archived from the original on 14 October 2005
noun
plural drop ins
1. Alternative spelling of drop-in.