"Impromptu gatherings" refers to informal and spontaneous get-togethers or social events that are planned or happen suddenly without prior preparation or organization. Full definition
For years this creamy crab salad has been my secret go - to recipe for impromptu gatherings with friends and family members -LSB-...] (themccallumsshamrockpatch.com)
The Techshow Summit was a fairly impromptu gathering of 40 - plus diverse leaders from many areas of our profession including academia, big and small firms, members of the judiciary, tech companies, legal service providers, insurance, local and national bar leaders and others. (rossintelligence.com)
Much of «Black Panther» was shot in and around the city, and the cast held impromptu gatherings at Wondaland. (nytimes.com)