1. A phrase, term, or way of speaking that follows strict rules of politeness, etiquette, or official language conventions
In business meetings, it is important to use formal expressions.
Em reuniões de negócios, é importante usar expressões formais.
2. In mathematics and logic, a symbolic representation or equation that follows established rules of notation
The mathematical formal expression was written on the blackboard.
A expressão formal matemática foi escrita no quadro negro.
3. A conventional or standardized way of communicating in official, academic, or professional contexts
The letter was written using formal expressions appropriate for official correspondence.
A carta foi escrita usando expressões formais apropriadas para correspondência oficial.