1. A spontaneous or unplanned exchange of items, roles, or positions between two or more people without prior arrangement
The two students decided on an impromptu swap of their lunch boxes.
Os dois alunos decidiram fazer uma troca improvisada de suas lancheiras.
2. An unscheduled exchange made on the spot, often casually or informally
They did an impromptu swap of phone numbers at the party.
Eles fizeram uma troca improvisada de números de telefone na festa.