1. A data field in a form, database, or software application that does not require user input and may be left blank
The phone number is an optional field in the registration form.
O número de telefone é um campo opcional no formulário de registro.
2. In programming and database design, a field that may or may not contain data without causing validation errors
The API accepts an optional field for user preferences.
A API aceita um campo opcional para preferências do usuário.