na-adjective
semiofficial; quasi-official
Describes an organization, role, or activity that is not fully official but has some official character or backing.
その団体は半官的な性格を持っている。
The organization has a semiofficial character.
彼は半官的な立場で会議に出
He attended the meeting in a semiofficial capacity.
非公式 means unofficial or informal, the opposite of 半官的 which still retains some official connection.
Compound of 半 (half) + 官 (government, official) + 的 (-like, -ish). The exact historical derivation is uncertain, but the word follows a common pattern for forming adjectives meaning 'semi-' or 'quasi-'.