drop by

Also, drop in or over. Pay a brief, casual, and usually unannounced visit. For example, I asked her to drop by whenever she was in the neighborhood, or Joan loves to have friends drop in, or We'd love to drop over but we haven't time on this trip. The first term dates from the first half of the 1900s; drop in is from the mid-1600s and drop over from the late 1800s.

The verb has one meaning:

Meaning #1: visit informally and spontaneously
  Synonyms: drop in, come by