1. An informal, one-time business exchange or deal that is not part of a regular or formal arrangement
The street vendor engaged in casual transactions with tourists throughout the day.
O vendedor de rua realizava transações casuais com turistas durante todo o dia.
2. A spontaneous or unplanned commercial interaction without legal documentation or formal agreement
They made a casual transaction for the used bicycle without any written contract.
Eles fizeram uma transação casual pela bicicleta usada sem nenhum contrato escrito.