1. an informal, unofficial, or spontaneous remark or notice about something without systematic study or formal analysis
Based on my casual observation, the store seems busier on weekends.
Pela minha observação casual, a loja parece mais movimentada nos fins de semana.
2. a passing comment or incidental notice made without deliberate attention or careful investigation
It was just a casual observation, nothing scientific.
Foi apenas uma observação casual, nada científico.