Use 'impromptu' when something surprising happens that requires immediate action without preparation. When the CEO visited, we had an impromptu meeting.
Pro Tip 2/3
Casual Feel
'Impromptu' often has a casual, laid-back connotation, suggesting a relaxed and unplanned nature. The impromptu beach volleyball game was a blast.
Pro Tip 3/3
Positive Surprise
Although unplanned, 'impromptu' can imply a pleasant and welcome surprise, like a spontaneous adventure. Her impromptu visit made my day.