1. A difficult problem that involves many interconnected parts, variables, or factors that are hard to understand or solve
Climate change is a complex problem that requires international cooperation.
A mudança climática é um problema complexo que requer cooperação internacional.
2. A situation or issue that cannot be resolved through simple or straightforward solutions
The housing crisis presents a complex problem with no easy answers.
A crise habitacional apresenta um problema complexo sem respostas fáceis.