This is the 649th most frequent Russian word.
официальный
Official.
Here 'официальный' describes a formal style or manner of communication.
Она всегда использует официальный тон в письмах.
She always uses an official tone in letters.
The word 'официальный' denotes something formal or related to being authoritative or institutional in nature.
Это был официальный визит президента.
This was an official visit of the president.
In this sentence, 'официальный' refers to something that adheres to a conventional or formal standard.