Drop round
Definition 1 of 1
Pro Tip 1/3Informal Visit
Used when you're going to see someone casually, without making formal plans. 
I might drop round for a few minutes to catch up.
Pro Tip 2/3Short Notice
Often implies that the visit wasn't planned long in advance; it can be spontaneous. 
If I finish early, I'll drop round to your place.
Pro Tip 3/3Quick Stay
Suggests the time spent during the visit will be brief. 
I just dropped round to pick up my book and left.