vestibule

Distantly related to the architectural vɛstɨbjuːl/ which is a small entrance hall or passage between the entrance and the interior of a building;

The contemporary vestibule is a short and often delightful experience that exists between two people in transition.
It typically transpires unexpectedly due to some form of serendipity and though short lived, is often quite lovely and/or memorable.

The term vestibule can alternatively be used to refer to any kind of furniture. odd architectural detail or small nook of unknown origin that defies other available description.

"Hey, are you dating that hotty i saw you with awhile back?"
"Yeah, no. but it was a pretty great vestibule."

"what do you call that thing?"
"that? hmmmmm.....I'm pretty sure it's a vestibule."