open letter
US /ˌoʊ.pən ˈlet̬.ɚ/
UK /ˌoʊ.pən ˈlet̬.ɚ/

1.
carta abierta
a letter of protest or appeal addressed to a particular person or group but intended for general publication
:
•
The activists published an open letter to the government.
Los activistas publicaron una carta abierta al gobierno.
•
Her open letter about climate change went viral.
Su carta abierta sobre el cambio climático se hizo viral.