1A personal seal used for routine approvals; an unregistered/informal stamp used instead of a registered seal.
宅配の受け取りは認印で済ませた。
I signed for the delivery with my personal seal (an informal stamp).
会社の備品申請は認印を押して提出してください。
Please submit the company equipment request with your personal seal.
重要な契約は実印を使い、簡単な届出には認印を使うことが多い。
Important contracts usually use a registered seal (jitsuin), while simple notifications often use a personal/unregistered seal.